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.

package-lock.json

@@ -7,6 +7,7 @@
       "name": "browser-cli-extension-build",
       "devDependencies": {
         "@types/chrome": "^0.1.40",
+        "@types/firefox-webext-browser": "^143.0.0",
         "esbuild": "^0.28.0",
         "typescript": "^6.0.3"
       }
@@ -481,6 +482,13 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/firefox-webext-browser": {
+      "version": "143.0.0",
+      "resolved": "https://registry.npmjs.org/@types/firefox-webext-browser/-/firefox-webext-browser-143.0.0.tgz",
+      "integrity": "sha512-865dYKMOP0CllFyHmgXV4IQgVL51OSQQCwSoihQ17EwugePKFSAZRc0EI+y7Ly4q7j5KyURlA7LgRpFieO4JOw==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@types/har-format": {
       "version": "1.2.16",
       "resolved": "https://registry.npmjs.org/@types/har-format/-/har-format-1.2.16.tgz",