diff --git a/@types/gecko.d.mts b/@types/gecko.d.mts
index 6c0ababc..996ea85f 100644
--- a/@types/gecko.d.mts
+++ b/@types/gecko.d.mts
@@ -247,8 +247,149 @@ interface nsIWindowMediator {
 
 declare var MozElements: MozElements;
 
-// TODO(glide-types)
-declare type BrowserTab = any;
+interface BrowserTab extends MozTabbrowserTab {
+  _glide_commandline: GlideCommandLine | null;
+}
+// Source browser/components/tabbrowser/content/tab.js
+interface MozTabbrowserTab extends XULElement {
+  // Source toolkit/content/customElements.js
+  disabled: boolean;
+  tabIndex: number;
+  // Source toolkit/content/customElements.js
+  label: string;
+  image: string;
+  command: string;
+  accessKey: string;
+  // Source toolkit/content/widgets/tabbox.js
+  value: string;
+  container: MozTabbrowserTabs;
+  control: MozTabbrowserTabs;
+  selected: boolean;
+  visible: boolean;
+  linkedPanel: string;
+  // Source browser/components/tabbrowser/content/tab.js
+  closing: boolean;
+  pinned: boolean;
+  isOpen: boolean;
+  readonly hidden: boolean;
+  muted: boolean;
+  multiselected: boolean;
+  userContextId: number;
+  soundPlaying: boolean;
+  pictureinpicture: boolean;
+  activeMediaBlocked: boolean;
+  undiscardable: boolean;
+  animationsEnabled: boolean;
+  isEmpty: boolean;
+  lastAccessed: number;
+  lastSeenActive: number;
+  attention: boolean;
+  owner: MozTabbrowserTab | null;
+  elementIndex: number;
+  group: MozTabbrowserTabGroup | null;
+  splitview: GlobalBrowser.MozTabSplitViewWrapper | null;
+  hasTabNote: boolean;
+  muteReason: string | undefined | null;
+
+  readonly overlayIcon: Element | null;
+  readonly audioButton: Element | null;
+  readonly throbber: Element | null;
+  readonly iconImage: Element | null;
+  readonly sharingIcon: Element | null;
+  readonly textLabel: Element | null;
+  readonly closeButton: Element | null;
+  readonly noteIcon: Element | null;
+  readonly noteIconOverlay: Element | null;
+
+  initialize(): void;
+  updateLastAccessed(date?: number): void;
+  updateLastSeenActive(): void;
+  updateLastUnloadedByTabUnloader(): void;
+  recordTimeFromUnloadToReload(): void;
+  toggleMuteAudio(muteReason?: string | null): void;
+  resumeDelayedMedia(): void;
+  setUserContextId(userContextId: number): void;
+  updateA11yDescription(): void;
+  updateSplitViewAriaLabel(index: number): void;
+  // Dynamically set by tabbrowser.js
+  linkedBrowser: GlobalBrowser.GlobalBrowser | null;
+  permanentKey: object | undefined;
+  description: string | undefined;
+  successor: MozTabbrowserTab | null;
+  predecessors: Set<MozTabbrowserTab>;
+  initializingTab: boolean | undefined;
+  openerTab: MozTabbrowserTab | undefined;
+  addedByAdoption: boolean | undefined;
+  removedByAdoption: boolean | undefined;
+  collapsed: boolean;
+}
+
+// Source browser/components/tabbrowser/content/tabgroup.js
+interface MozTabbrowserTabGroup extends XULElement {
+  overflowContainer: XULElement;
+  saveOnWindowClose: boolean;
+
+  color: string;
+  defaultGroupName: string;
+  id: string;
+  hasActiveTab: boolean;
+  label: string;
+  name: string;
+  collapsed: boolean;
+  lastSeenActive: number;
+  tabs: MozTabbrowserTab[];
+  tabsAndSplitViews: (MozTabbrowserTab | GlobalBrowser.MozTabSplitViewWrapper)[];
+  labelElement: Element;
+  labelContainerElement: XULElement;
+  overflowCountLabel: Element;
+  wasCreatedByAdoption: boolean;
+  isBeingDragged: boolean;
+  hoverPreviewPanelActive: boolean;
+
+  addTabs(
+    tabsOrSplitViews: (MozTabbrowserTab | GlobalBrowser.MozTabSplitViewWrapper)[],
+    metricsContext?: object,
+  ): void;
+  ungroupTabs(metricsContext?: object): void;
+  save(options?: object): void;
+  saveAndClose(options?: object): void;
+  select(): void;
+  isTabVisibleInGroup(tab: MozTabbrowserTab): boolean;
+}
+
+// Source browser/components/tabbrowser/content/tabs.js
+interface MozTabbrowserTabs extends XULElement {
+  startupTime: number;
+  arrowScrollbox: Element;
+  pinnedTabsContainer: Element;
+  previewPanel: object | null;
+  tooltip: string;
+  tabDragAndDrop: object;
+  emptyTabTitle: string;
+  tabbox: XULElement;
+  newTabButton: Element;
+  verticalMode: boolean;
+  expandOnHover: boolean;
+  overflowing: boolean;
+  allTabs: MozTabbrowserTab[];
+  allGroups: MozTabbrowserTabGroup[];
+  allSplitViews: MozTabSplitViewWrapper[];
+  openTabs: MozTabbrowserTab[];
+  nonHiddenTabs: MozTabbrowserTab[];
+  visibleTabs: MozTabbrowserTab[];
+  tablistHasFocus: boolean;
+  ariaFocusableItems: Element[];
+  dragAndDropElements: Element[];
+  init(): void;
+  destroy(): void;
+  advanceSelectedItem(direction: number, wrap: boolean): void;
+  ensureTabPreviewPanelLoaded(): Promise<void>;
+  updateTabSoundLabel(tab: MozTabbrowserTab): void;
+  getRelatedElement(tab: MozTabbrowserTab): Element;
+  isContainerVerticalPinnedGrid(tab: MozTabbrowserTab): boolean;
+  cancelTabGroupPreview(): void;
+  showTabGroupPreview(group: MozTabbrowserTabGroup): void;
+}
 
 declare var GlideBrowser: typeof import("../src/glide/browser/base/content/browser.mts").GlideBrowser;
 
diff --git a/src/glide/browser/base/content/GlideTestUtils.sys.mts b/src/glide/browser/base/content/GlideTestUtils.sys.mts
index d47a942e..d38a499f 100644
--- a/src/glide/browser/base/content/GlideTestUtils.sys.mts
+++ b/src/glide/browser/base/content/GlideTestUtils.sys.mts
@@ -50,7 +50,7 @@ class GlideTestUtilsClass {
    * Behaves the same as `BrowserTestUtils.openNewForegroundTab()` but also defines
    * `[Symbol.dispose]()` so you can use it with `using`.
    */
-  async new_tab(uri?: string): Promise<BrowserTab> {
+  async new_tab(uri?: string): Promise<BrowserTab & Disposable> {
     const tab = await g.BrowserTestUtils.openNewForegroundTab(g.gBrowser, uri);
     return Object.assign(tab, {
       [Symbol.dispose]() {
diff --git a/src/glide/browser/base/content/browser-commandline.mts b/src/glide/browser/base/content/browser-commandline.mts
index f58f33ad..94100cc9 100644
--- a/src/glide/browser/base/content/browser-commandline.mts
+++ b/src/glide/browser/base/content/browser-commandline.mts
@@ -210,7 +210,7 @@ export class TabsCompletionSource implements GlideCompletionSource<TabCompletion
                 tab.label,
               ],
             }),
-            DOM.create_element("td", { className: "url", children: tab.linkedBrowser.currentURI.spec }),
+            DOM.create_element("td", { className: "url", children: tab.linkedBrowser?.currentURI.spec }),
           ],
         }),
 
diff --git a/src/glide/browser/base/content/browser-excmds.mts b/src/glide/browser/base/content/browser-excmds.mts
index fbbddd3d..8c806f57 100644
--- a/src/glide/browser/base/content/browser-excmds.mts
+++ b/src/glide/browser/base/content/browser-excmds.mts
@@ -293,7 +293,7 @@ class GlideExcmdsClass {
       }
 
       case "tab_next": {
-        const all_tabs = gBrowser.tabContainer.allTabs as unknown[];
+        const all_tabs = gBrowser.tabContainer.allTabs;
         let next_index = gBrowser.tabContainer.selectedIndex + 1;
         if (next_index >= all_tabs.length) {
           next_index = 0;
@@ -349,6 +349,9 @@ class GlideExcmdsClass {
 
       case "tab_pin_toggle": {
         const tab = gBrowser.selectedTab;
+        if (!tab) {
+          throw new Error("No tab to pin/unpin");
+        }
         if (tab.pinned) {
           gBrowser.unpinTab(tab);
         } else {
@@ -363,6 +366,9 @@ class GlideExcmdsClass {
       }
 
       case "tab_duplicate": {
+        if (!gBrowser.selectedTab) {
+          throw new Error("No tab to duplicate");
+        }
         gBrowser.duplicateTab(gBrowser.selectedTab, undefined, { inBackground: false });
         break;
       }
diff --git a/src/glide/browser/base/content/browser.mts b/src/glide/browser/base/content/browser.mts
index 5ceadfb2..03d32c8b 100644
--- a/src/glide/browser/base/content/browser.mts
+++ b/src/glide/browser/base/content/browser.mts
@@ -893,7 +893,9 @@ class GlideBrowserClass {
         url: location.spec,
         get tab_id() {
           return assert_present(
-            GlideBrowser.extension.tabManager.getWrapper(gBrowser.selectedTab),
+            GlideBrowser.extension.tabManager.getWrapper(
+              assert_present(gBrowser.selectedTab, "could not resolve selected tab"),
+            ),
             "could not resolve tab wrapper",
           ).id;
         },
@@ -1899,6 +1901,9 @@ class GlideBrowserClass {
    */
   async upsert_commandline(opts: GlideCommandLineShowOptions = {}) {
     const tab = gBrowser.selectedTab;
+    if (!tab) {
+      return null;
+    }
     const cached = this.#get_cached_commandline(tab);
     if (cached) {
       cached.show(opts);
@@ -1931,6 +1936,9 @@ class GlideBrowserClass {
   }
 
   async toggle_commandline() {
+    if (!gBrowser.selectedTab) {
+      return;
+    }
     const commandline = this.#get_cached_commandline(gBrowser.selectedTab);
     if (!commandline) {
       await this.upsert_commandline();
@@ -1950,6 +1958,9 @@ class GlideBrowserClass {
    * This only returns anything **if** the commandline is open **and** it is focused.
    */
   #get_active_commandline(): GlideCommandLine | null {
+    if (!gBrowser.selectedTab) {
+      return null;
+    }
     const commandline = this.#get_cached_commandline(gBrowser.selectedTab);
     if (!commandline) {
       return null;
@@ -1971,6 +1982,9 @@ class GlideBrowserClass {
   }
 
   get_commandline(): GlideCommandLine | null {
+    if (!gBrowser.selectedTab) {
+      return null;
+    }
     return this.#get_cached_commandline(gBrowser.selectedTab);
   }
 
@@ -1982,7 +1996,7 @@ class GlideBrowserClass {
     return tab._glide_commandline;
   }
 
-  #cache_commandline(tab: BrowserTab, excmdbar: Element): void {
+  #cache_commandline(tab: BrowserTab, excmdbar: GlideCommandLine): void {
     tab._glide_commandline = excmdbar;
   }
 }
diff --git a/src/glide/browser/base/content/test/config/browser_options.ts b/src/glide/browser/base/content/test/config/browser_options.ts
index 9b1dcac0..dda49558 100644
--- a/src/glide/browser/base/content/test/config/browser_options.ts
+++ b/src/glide/browser/base/content/test/config/browser_options.ts
@@ -26,6 +26,9 @@ async function newtab() {
 
   return {
     [Symbol.dispose]() {
+      if (!tab) {
+        return;
+      }
       gBrowser.removeTab(tab);
     },
   };
diff --git a/src/glide/browser/base/content/test/excmds/browser_excmds.ts b/src/glide/browser/base/content/test/excmds/browser_excmds.ts
index ebbd960c..4a2915ae 100644
--- a/src/glide/browser/base/content/test/excmds/browser_excmds.ts
+++ b/src/glide/browser/base/content/test/excmds/browser_excmds.ts
@@ -21,7 +21,10 @@ function current_url() {
 }
 
 add_task(async function test_tab_switching() {
-  const browser = gBrowser.tabContainer.allTabs.at(0).linkedBrowser;
+  const browser = gBrowser.tabContainer.allTabs.at(0)?.linkedBrowser;
+  if (!browser) {
+    throw new Error("No browser found");
+  }
   BrowserTestUtils.startLoadingURIString(browser, INPUT_TEST_FILE + "?i=0");
   await BrowserTestUtils.browserLoaded(browser);
   using _tab2 = await GlideTestUtils.new_tab(INPUT_TEST_FILE + "?i=1");
@@ -274,9 +277,9 @@ add_task(async function test_tab_pin() {
   using tab1 = await GlideTestUtils.new_tab(INPUT_TEST_FILE + "?i=1");
   using _tab2 = await GlideTestUtils.new_tab(INPUT_TEST_FILE + "?i=2");
 
-  is(gBrowser.selectedTab.pinned, false, "Current tab should not be pinned initially");
+  is(gBrowser.selectedTab!.pinned, false, "Current tab should not be pinned initially");
   await keys(":tab_pin<CR>");
-  is(gBrowser.selectedTab.pinned, true, "Current tab should be pinned after :tab_pin");
+  is(gBrowser.selectedTab!.pinned, true, "Current tab should be pinned after :tab_pin");
 
   const tab1_id = GlideBrowser.extension?.tabManager?.getWrapper?.(tab1)?.id;
   isnot(tab1_id, undefined, "Tab ID should be available");
@@ -294,11 +297,11 @@ add_task(async function test_tab_unpin() {
   using tab1 = await GlideTestUtils.new_tab(INPUT_TEST_FILE + "?i=1");
   using _tab2 = await GlideTestUtils.new_tab(INPUT_TEST_FILE + "?i=2");
 
-  gBrowser.pinTab(gBrowser.selectedTab);
+  gBrowser.pinTab(gBrowser.selectedTab!);
 
-  is(gBrowser.selectedTab.pinned, true, "Current tab should be pinned initially");
+  is(gBrowser.selectedTab!.pinned, true, "Current tab should be pinned initially");
   await keys(":tab_unpin<CR>");
-  is(gBrowser.selectedTab.pinned, false, "Current tab should be unpinned after :tab_unpin");
+  is(gBrowser.selectedTab!.pinned, false, "Current tab should be unpinned after :tab_unpin");
 
   gBrowser.pinTab(tab1);
   const tab1_id = GlideBrowser.extension?.tabManager?.getWrapper?.(tab1)?.id;
@@ -316,15 +319,15 @@ add_task(async function test_tab_pin_toggle_excmd() {
   using tab = await GlideTestUtils.new_tab(KEY_TEST_FILE + "?i=1");
   const initial_tab_count = gBrowser.tabs.length;
   is(gBrowser.selectedTab, tab);
-  is(gBrowser.selectedTab.pinned, false, "Current tab should not be pinned initially");
+  is(gBrowser.selectedTab!.pinned, false, "Current tab should not be pinned initially");
 
   await keys(":tab_pin_toggle<CR>");
 
   is(gBrowser.tabs.length, initial_tab_count, "Tab count should remain the same");
-  is(gBrowser.selectedTab.pinned, true, "Current tab should be pinned after :tab_pin_toggle");
+  is(gBrowser.selectedTab!.pinned, true, "Current tab should be pinned after :tab_pin_toggle");
 
   await keys(":tab_pin_toggle<CR>");
-  is(gBrowser.selectedTab.pinned, false, "Current tab should be unpinned after :tab_pin_toggle");
+  is(gBrowser.selectedTab!.pinned, false, "Current tab should be unpinned after :tab_pin_toggle");
   is(gBrowser.tabs.length, initial_tab_count, "Tab count should remain the same");
 });
 
@@ -334,7 +337,7 @@ add_task(async function test_tab_pin_toggle_keymap() {
   using tab = await GlideTestUtils.new_tab(KEY_TEST_FILE + "?i=1");
   const initial_tab_count = gBrowser.tabs.length;
   is(gBrowser.selectedTab, tab);
-  is(gBrowser.selectedTab.pinned, false, "Current tab should not be pinned initially");
+  is(gBrowser.selectedTab!.pinned, false, "Current tab should not be pinned initially");
 
   await keys("<esc>");
   await wait_for_mode("normal");
@@ -342,10 +345,10 @@ add_task(async function test_tab_pin_toggle_keymap() {
   await keys("<A-p>");
   is(gBrowser.tabs.length, initial_tab_count, "Tab count should remain the same");
 
-  await waiter(() => gBrowser.selectedTab.pinned).is(true, "Tab should be pinned after <A-p>");
+  await waiter(() => gBrowser.selectedTab!.pinned).is(true, "Tab should be pinned after <A-p>");
 
   await keys("<A-p>");
-  await waiter(() => gBrowser.selectedTab.pinned).is(false, "Tab should be unpinned after <A-p>");
+  await waiter(() => gBrowser.selectedTab!.pinned).is(false, "Tab should be unpinned after <A-p>");
   is(gBrowser.tabs.length, initial_tab_count, "Tab count should remain the same");
 });
 
@@ -355,7 +358,7 @@ add_task(async function test_tab_reopen() {
   const initial_tab_count = gBrowser.tabs.length;
   const test_url = INPUT_TEST_FILE + "?reopen_test";
 
-  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, test_url);
+  using tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, test_url);
   is(gBrowser.tabs.length, initial_tab_count + 1, "New tab should be created");
   is(current_url(), test_url, "New tab should have the test URL");
 
diff --git a/src/glide/browser/base/content/test/hints/browser_hints.ts b/src/glide/browser/base/content/test/hints/browser_hints.ts
index 07457ebd..7ff7c5a8 100644
--- a/src/glide/browser/base/content/test/hints/browser_hints.ts
+++ b/src/glide/browser/base/content/test/hints/browser_hints.ts
@@ -94,7 +94,7 @@ add_task(async function test_F_opens_new_tab() {
     is(GlideBrowser.state.mode, "normal", "Mode should return to 'normal' after following hint");
 
     if (final_tab_count > initial_tab_count) {
-      gBrowser.removeTab(gBrowser.selectedTab);
+      gBrowser.removeTab(gBrowser.selectedTab!);
     }
   });
 });
@@ -438,7 +438,7 @@ add_task(async function test_numeric_hint_generator() {
     is(GlideBrowser.state.mode, "normal", "Mode should return to 'normal' after following hint");
 
     if (final_tab_count > initial_tab_count) {
-      gBrowser.removeTab(gBrowser.selectedTab);
+      gBrowser.removeTab(gBrowser.selectedTab!);
     }
   });
 });
diff --git a/src/glide/browser/base/content/test/navigation/browser_jumplist.ts b/src/glide/browser/base/content/test/navigation/browser_jumplist.ts
index 0429b316..62a066a1 100644
--- a/src/glide/browser/base/content/test/navigation/browser_jumplist.ts
+++ b/src/glide/browser/base/content/test/navigation/browser_jumplist.ts
@@ -18,7 +18,10 @@ function current_url() {
 }
 
 add_task(async function test_jumplist_basic_navigation() {
-  const browser = gBrowser.tabContainer.allTabs.at(0).linkedBrowser;
+  const browser = gBrowser.tabContainer.allTabs.at(0)?.linkedBrowser;
+  if (!browser) {
+    throw new Error("No browser found");
+  }
   BrowserTestUtils.startLoadingURIString(browser, uri(0));
   await BrowserTestUtils.browserLoaded(browser);
 
@@ -47,7 +50,10 @@ add_task(async function test_jumplist_basic_navigation() {
 });
 
 add_task(async function test_jumplist_prunes_forward_slice() {
-  const browser = gBrowser.tabContainer.allTabs.at(0).linkedBrowser;
+  const browser = gBrowser.tabContainer.allTabs.at(0)?.linkedBrowser;
+  if (!browser) {
+    throw new Error("No browser found");
+  }
   BrowserTestUtils.startLoadingURIString(browser, uri(0));
   await BrowserTestUtils.browserLoaded(browser);
 
@@ -68,7 +74,10 @@ add_task(async function test_jumplist_prunes_forward_slice() {
 });
 
 add_task(async function test_jumplist_max_entries_trim() {
-  const browser = gBrowser.tabContainer.allTabs.at(0).linkedBrowser;
+  const browser = gBrowser.tabContainer.allTabs.at(0)?.linkedBrowser;
+  if (!browser) {
+    throw new Error("No browser found");
+  }
   BrowserTestUtils.startLoadingURIString(browser, uri(0));
   await BrowserTestUtils.browserLoaded(browser);
 
@@ -102,7 +111,10 @@ add_task(async function test_jumplist_max_entries_trim() {
 });
 
 add_task(async function test_jumplist_deleted_intermediary_tab() {
-  const browser = gBrowser.tabContainer.allTabs.at(0).linkedBrowser;
+  const browser = gBrowser.tabContainer.allTabs.at(0)?.linkedBrowser;
+  if (!browser) {
+    throw new Error("No browser found");
+  }
   BrowserTestUtils.startLoadingURIString(browser, uri(0));
   await BrowserTestUtils.browserLoaded(browser);