diff --git a/src/background/commands.mjs b/src/background/commands.mjs
index 1440d74d..cba9f7db 100644
--- a/src/background/commands.mjs
+++ b/src/background/commands.mjs
@@ -12,15 +12,58 @@ export function registerCommands() {
 
     if (command in menuConfig) {
       if (menuConfig[command].action) {
-        menuConfig[command].action(true, tab)
+        // The action may return a Promise (e.g. openSidePanel returns the
+        // chrome.sidePanel.open() Promise). Keep the call synchronous so the
+        // user-gesture context is preserved, but observe the Promise so a
+        // rejection does not become an unhandled rejection in the background.
+        // Also wrap in try/catch because Browser.commands.onCommand documents
+        // `tab` as optional, so an action that dereferences tab.* (e.g. the
+        // openSidePanel call) can throw synchronously.
+        let result
+        try {
+          result = menuConfig[command].action(true, tab)
+        } catch (error) {
+          console.error(`failed to run command action "${command}"`, error)
+          return
+        }
+        if (result && typeof result.catch === 'function') {
+          result.catch((error) => {
+            console.error(`failed to run command action "${command}"`, error)
+          })
+        }
       }
 
       if (menuConfig[command].genPrompt) {
-        const currentTab = (await Browser.tabs.query({ active: true, currentWindow: true }))[0]
-        Browser.tabs.sendMessage(currentTab.id, {
-          type: 'CREATE_CHAT',
-          data: message,
-        })
+        // Mirror the pattern in menus.mjs so no step here can leak an
+        // unhandled rejection in the background:
+        //   - Browser.tabs.query() can reject (permission errors, etc.) —
+        //     observe via try/catch.
+        //   - tabs[0] may be undefined when no active tab exists — guard
+        //     before dereferencing currentTab.id.
+        //   - Browser.tabs.sendMessage() (via webextension-polyfill) rejects
+        //     in normal extension usage (no content script listening,
+        //     restricted pages like chrome://, stale content scripts after
+        //     extension reload) — attach a .catch().
+        let tabs
+        try {
+          tabs = await Browser.tabs.query({ active: true, currentWindow: true })
+        } catch (error) {
+          console.error(`failed to query active tab for command "${command}"`, error)
+          return
+        }
+        const currentTab = tabs && tabs[0]
+        if (!currentTab) {
+          console.debug(`command "${command}" triggered but no active tab found, skipping`)
+          return
+        }
+        Browser.tabs
+          .sendMessage(currentTab.id, {
+            type: 'CREATE_CHAT',
+            data: message,
+          })
+          .catch((error) => {
+            console.error(`failed to send CREATE_CHAT message for command "${command}"`, error)
+          })
       }
     }
   })
diff --git a/src/background/menus.mjs b/src/background/menus.mjs
index a92bd7ba..d3a61ee1 100644
--- a/src/background/menus.mjs
+++ b/src/background/menus.mjs
@@ -5,33 +5,107 @@ import { config as menuConfig } from '../content-script/menu-tools/index.mjs'
 
 const menuId = 'ChatGPTBox-Menu'
 const onClickMenu = (info, tab) => {
-  Browser.tabs.query({ active: true, currentWindow: true }).then((tabs) => {
-    const currentTab = tabs[0]
-    const message = {
-      itemId: info.menuItemId.replace(menuId, ''),
-      selectionText: info.selectionText,
-      useMenuPosition: tab.id === currentTab.id,
-    }
-    console.debug('menu clicked', message)
+  const itemId = info.menuItemId.replace(menuId, '')
 
-    if (defaultConfig.selectionTools.includes(message.itemId)) {
-      Browser.tabs.sendMessage(currentTab.id, {
-        type: 'CREATE_CHAT',
-        data: message,
+  // sidePanel.open() must be called synchronously within the user gesture handler.
+  // Calling it inside a Promise callback (e.g. Browser.tabs.query().then()) breaks
+  // Chrome's user gesture requirement and causes the error:
+  // "sidePanel.open() may only be called in response to a user gesture."
+  if (itemId === 'openSidePanel' && menuConfig.openSidePanel?.action) {
+    // Keep the call synchronous to preserve the user-gesture requirement,
+    // but observe the returned Promise so a rejected sidePanel.open() does
+    // not become an unhandled rejection in the background script.
+    // Also wrap in try/catch because contextMenus.onClicked documents `tab`
+    // as optional ("If the click did not take place in a tab, this parameter
+    // will be missing"), so the openSidePanel action that dereferences
+    // tab.windowId/tab.id can throw synchronously.
+    let result
+    try {
+      result = menuConfig.openSidePanel.action(true, tab)
+    } catch (error) {
+      console.error('failed to open side panel', error)
+      return
+    }
+    if (result && typeof result.catch === 'function') {
+      result.catch((error) => {
+        console.error('failed to open side panel', error)
       })
-    } else if (message.itemId in menuConfig) {
-      if (menuConfig[message.itemId].action) {
-        menuConfig[message.itemId].action(true, tab)
+    }
+    return
+  }
+
+  Browser.tabs
+    .query({ active: true, currentWindow: true })
+    .then((tabs) => {
+      const currentTab = tabs && tabs[0]
+      if (!currentTab) {
+        console.debug('menu clicked but no active tab found, skipping')
+        return
       }
 
-      if (menuConfig[message.itemId].genPrompt) {
-        Browser.tabs.sendMessage(currentTab.id, {
-          type: 'CREATE_CHAT',
-          data: message,
-        })
+      // contextMenus.onClicked documents `tab` as optional ("If the click did
+      // not take place in a tab, this parameter will be missing"), so guard
+      // before dereferencing tab.id when computing useMenuPosition.
+      const message = {
+        itemId,
+        selectionText: info.selectionText,
+        useMenuPosition: tab ? tab.id === currentTab.id : false,
       }
-    }
-  })
+      console.debug('menu clicked', message)
+
+      if (defaultConfig.selectionTools.includes(message.itemId)) {
+        // Browser.tabs.sendMessage() (via webextension-polyfill) returns a
+        // Promise that commonly rejects (no content script listening, restricted
+        // pages such as chrome://, stale content scripts after extension reload)
+        // — observe it so we don't leak unhandled rejections in the background.
+        Browser.tabs
+          .sendMessage(currentTab.id, {
+            type: 'CREATE_CHAT',
+            data: message,
+          })
+          .catch((error) => {
+            console.error(`failed to send CREATE_CHAT message for "${message.itemId}"`, error)
+          })
+      } else if (message.itemId in menuConfig) {
+        if (menuConfig[message.itemId].action) {
+          // Several actions in menuConfig are async (e.g. tabs/windows calls)
+          // and can throw synchronously or return a rejected Promise. Mirror
+          // the handling already used for openSidePanel above and in
+          // commands.mjs so neither path leaks an unhandled rejection in the
+          // background script.
+          let actionResult
+          try {
+            actionResult = menuConfig[message.itemId].action(true, tab)
+          } catch (error) {
+            console.error(`failed to run menu action "${message.itemId}"`, error)
+          }
+          if (actionResult && typeof actionResult.catch === 'function') {
+            actionResult.catch((error) => {
+              console.error(`failed to run menu action "${message.itemId}"`, error)
+            })
+          }
+        }
+
+        if (menuConfig[message.itemId].genPrompt) {
+          // Same rationale as the sendMessage call above — observe the Promise
+          // so a rejected sendMessage (no content script, restricted page, etc.)
+          // doesn't surface as an unhandled rejection in the background.
+          Browser.tabs
+            .sendMessage(currentTab.id, {
+              type: 'CREATE_CHAT',
+              data: message,
+            })
+            .catch((error) => {
+              console.error(`failed to send CREATE_CHAT message for "${message.itemId}"`, error)
+            })
+        }
+      }
+    })
+    .catch((error) => {
+      // Browser.tabs.query() can reject (e.g. on permission errors); make sure
+      // it does not become an unhandled promise rejection in the background.
+      console.error('failed to query active tab for menu click', error)
+    })
 }
 export function refreshMenu() {
   if (Browser.contextMenus.onClicked.hasListener(onClickMenu))
diff --git a/src/content-script/menu-tools/index.mjs b/src/content-script/menu-tools/index.mjs
index 0f46392e..f777b525 100644
--- a/src/content-script/menu-tools/index.mjs
+++ b/src/content-script/menu-tools/index.mjs
@@ -59,14 +59,29 @@ export const config = {
   },
   openSidePanel: {
     label: 'Open Side Panel',
-    action: async (fromBackground, tab) => {
+    action: (fromBackground, tab) => {
       console.debug('action is from background', fromBackground)
       if (fromBackground) {
         // eslint-disable-next-line no-undef
-        chrome.sidePanel.open({ windowId: tab.windowId, tabId: tab.id })
-      } else {
-        // side panel is not supported
+        if (typeof chrome === 'undefined' || !chrome.sidePanel?.open) {
+          // sidePanel API is not available in this browser (e.g. Firefox)
+          return Promise.reject(new Error('chrome.sidePanel API is not available'))
+        }
+        // contextMenus.onClicked / commands.onCommand document `tab` as
+        // optional, and even when present the tab may not have an id or
+        // windowId (e.g. clicks outside a normal browser tab). Guard here so
+        // callers do not have to wrap every invocation in try/catch just to
+        // avoid a TypeError from dereferencing tab.windowId / tab.id.
+        if (!tab || tab.windowId == null || tab.id == null) {
+          return Promise.reject(
+            new Error('chrome.sidePanel.open requires a tab with windowId and id'),
+          )
+        }
+        // eslint-disable-next-line no-undef
+        return chrome.sidePanel.open({ windowId: tab.windowId, tabId: tab.id })
       }
+      // side panel is not supported
+      return undefined
     },
   },
   closeAllChats: {