diff --git a/extension/src/background.ts b/extension/src/background.ts
index 40645536..29b0aace 100644
--- a/extension/src/background.ts
+++ b/extension/src/background.ts
@@ -3,7 +3,7 @@ import browser from "webextension-polyfill"
 import type {BrowserAction, Menus, PageAction, Runtime, Tabs, WebNavigation} from "webextension-polyfill"
 
 import type {Url, SearchPageParams} from './common'
-import {Visit, Visits, Blacklisted, Methods, uuid} from './common'
+import {Visit, Visits, Blacklisted, Methods, assert, uuid} from './common'
 import type {Options} from './options'
 import {Toggles, getOptions, setOption, THIS_BROWSER_TAG} from './options'
 
@@ -666,7 +666,10 @@ export async function handleToggleSidebar() {
 function registerActions() {
     // NOTE: on mobile, this sets action for both icon (if it's displayed) and in the menu
     for (const action of actions()) {
-        action.onClicked.addListener(defensify(toggleSidebarOnTab, 'action.onClicked'))
+        action.onClicked.addListener(defensify(
+            (tab: Tabs.Tab) => toggleSidebarOnTab({url: tab.url!, id: tab.id!}),
+            'action.onClicked',
+        ))
     }
 }
 
@@ -689,12 +692,6 @@ const onCommandCallback = defensify(async cmd => {
 }, 'onCommand')
 
 
-type MenuInfo = {
-    menuItemId: string,
-    linkUrl?: string,
-}
-
-
 async function active(): Promise<TabUrl> {
     return (await getActiveTab())!
 }
@@ -844,7 +841,7 @@ ${surl}
             },
         )
     },
-    onMenuClick: async function(info: MenuInfo, _tab: Tabs.Tab) {
+    onMenuClick: async function(info: Menus.OnClickData, _tab: Tabs.Tab) {
         const url = info.linkUrl!
         await AddToMarkVisitedExcludelist.add([url])
     },
@@ -858,7 +855,7 @@ const DEFAULT_CONTEXTS: Array<Menus.ContextType> = ['page', 'browser_action']
 type MenuEntry = {
     id: string,
     title: string,
-    callback: ((info: MenuInfo, tab: Tabs.Tab) => Promise<void>) | null,
+    callback: ((info: Menus.OnClickData, tab: Tabs.Tab) => Promise<void>) | null,
     contexts?: Array<Menus.ContextType>, // NOTE: not present interpreted as DEFAULT_CONTEXTS
     parentId?: string,
 }
@@ -977,7 +974,8 @@ function initContextMenus(): void {
     })
 
     // need to keep these callbacks here, since onInstalled above isn't called when background page resumes
-    const onMenuClickedCallback = defensify(async (info: MenuInfo, tab: Tabs.Tab) => {
+    const onMenuClickedCallback = defensify(async (info: Menus.OnClickData, tab: Tabs.Tab | undefined) => {
+        assert(tab != null)
         const mid = info.menuItemId
         for (const m of [...MENUS, ...TOGGLES]) {
             if (mid == m.id) {
diff --git a/extension/src/common.ts b/extension/src/common.ts
index d6220e9e..06de18d1 100644
--- a/extension/src/common.ts
+++ b/extension/src/common.ts
@@ -326,3 +326,11 @@ export function getOrDefault<T>(obj: any, key: string, def: T): T {
     const res = obj[key];
     return res === undefined ? def : res;
 }
+
+
+// js doesn't have builtin assert :(
+export function assert(condition: any, msg?: string): asserts condition {
+    if (!condition) {
+        throw new Error(`assertion failed ${msg}`)
+    }
+}
diff --git a/extension/src/notifications.ts b/extension/src/notifications.ts
index 0036d6e7..8469f096 100644
--- a/extension/src/notifications.ts
+++ b/extension/src/notifications.ts
@@ -42,10 +42,12 @@ export function alertError(obj: any) {
 }
 
 
-// TODO see if I can define a typescript tyoe..
-// @ts-expect-error
-export function defensify(pf: (...any) => Promise<any>, name: string): (...any) => Promise<void> {
-    const fname = pf.name // hopefully it's always present?
+type DefensifyArgs = readonly unknown[]
+export function defensify<Args extends DefensifyArgs>(
+    pf: (...args: Args) => Promise<any>,
+    name: string,
+): (...args: Args) => Promise<void> {
+    const fname = pf.name  // hopefully it's always present?
     const error_handler = (err: Error) => {
         console.error('function "%s" %s failed: %o', fname, name, err)
         getOptions().then((opts: Options) => {
@@ -56,17 +58,18 @@ export function defensify(pf: (...any) => Promise<any>, name: string): (...any)
             }
         })
     }
-    return (...args) => pf(...args).then(() => {
+    return (...args: Args) => pf(...args).then(() => {
         // suppress return values, since the defensive error handler 'erases; the type anyway'
         return
     }).catch(error_handler)
 }
 
 
-// TODO return type should be void here too...
-// @ts-expect-error
-export function defensifyAlert(pf: (...any) => Promise<any>): (any) => Promise<any> {
-    return (...args) => pf(...args).catch(alertError);
+type DefensifyAlertArgs = readonly unknown[]
+export function defensifyAlert<Args extends DefensifyAlertArgs>(
+    pf: (...args: Args) => Promise<any>,
+): (...args: Args) => Promise<void> {
+    return (...args) => pf(...args).catch(alertError)
 }
 
 
diff --git a/extension/tsconfig.json b/extension/tsconfig.json
index 149d1033..da715852 100644
--- a/extension/tsconfig.json
+++ b/extension/tsconfig.json
@@ -10,6 +10,9 @@
     "moduleResolution": "bundler",
     // esnext is necessary, otherwise bundler module resolution can't be used?
     "module": "esnext",
+
+    // without it, emacs (LSP?) complains when editing files.. not sure if impacts actual code generation?
+    "lib": ["es6", "dom"],
   },
   "include": [
     "./src/**/*.ts"