feat(extension): add Firefox WebExtension support

- Add a neutral WebExtension API adapter that uses Firefox browser.* or Chromium chrome.* without mutating globals.
- Switch extension runtime code to the adapter and add Firefox-specific typings for tabs, windows, tab groups, storage, scripting, and native messaging ports.
- Fix Firefox temporary add-on instructions to load the packaged manifest with background.scripts instead of the Chromium service worker manifest.
- Detect Firefox in clients.list via runtime.getBrowserInfo and keep Chromium user-agent fallback support.
- Make navigate.open wait briefly for Firefox to replace initial about:blank with the requested URL.
- Add JS coverage for API selection, clients.list browser detection, and Firefox navigate.open URL polling.
- Bump package and extension version to 0.15.2.

extension/src/commands/extension.ts

@@ -1,3 +1,4 @@
+import { webExtApi as api } from '../browser-api';
 import { CommandGroup } from '../classes/CommandGroup';
 import type { CommandEntry } from '../classes/CommandGroup';
 
@@ -5,7 +6,7 @@ export class ExtensionCommands extends CommandGroup {
   readonly namespace = "extension";
   readonly commands: Record<string, CommandEntry> = {
     "extension.reload": () => {
-      setTimeout(() => chrome.runtime.reload(), 200);
+      setTimeout(() => api.runtime.reload(), 200);
       return { reloading: true };
     },
     "extension.info": () => this.extensionInfo(),
@@ -29,9 +30,9 @@ export class ExtensionCommands extends CommandGroup {
   }
 
   private extensionInfo() {
-    const manifest = chrome.runtime.getManifest();
+    const manifest = api.runtime.getManifest();
     return {
-      id: chrome.runtime.id,
+      id: api.runtime.id,
       name: manifest.name,
       version: manifest.version,
       manifestVersion: manifest.manifest_version,