Add Firefox compatibility layer and improve API detection

Introduces firefox-compat.js to handle Firefox-specific messaging and storage, and updates background.js and popup.js to robustly detect and use the appropriate extension APIs for both Chrome and Firefox environments. Manifest and popup files are updated to load the new compatibility script, ensuring reliable settings management and messaging across browsers.

manifest-firefox.json

@@ -1,31 +1,27 @@
 {
-  "manifest_version": 2,
-  "name": "Xget Now",
-  "version": "2.0.4",
-  "description": "为 Firefox 浏览器提供的 Xget 下载加速扩展，支持 GitHub、GitLab、npm、PyPI 等众多平台的文件下载加速",
+  "background": {
+    "persistent": true,
+    "scripts": ["webext-compat.js", "background.js"]
+  },
   "browser_action": {
     "default_icon": {
+      "128": "icons/icon128.png",
       "16": "icons/icon16.png",
       "32": "icons/icon32.png",
-      "48": "icons/icon48.png",
-      "128": "icons/icon128.png"
+      "48": "icons/icon48.png"
     },
     "default_popup": "popup.html",
     "default_title": "Xget Now"
   },
-  "background": {
-    "scripts": [
-      "webext-compat.js",
-      "background.js"
-    ],
-    "persistent": false
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "i@xi-xu.me",
+      "strict_min_version": "109.0"
+    }
   },
   "content_scripts": [
     {
-      "js": [
-        "webext-compat.js",
-        "content.js"
-      ],
+      "js": ["webext-compat.js", "content.js"],
       "matches": [
         "https://github.com/*",
         "https://gitlab.com/*",
@@ -56,6 +52,15 @@
       "run_at": "document_end"
     }
   ],
+  "description": "为 Firefox 浏览器提供的 Xget 下载加速扩展，支持 GitHub、GitLab、npm、PyPI 等众多平台的文件下载加速",
+  "icons": {
+    "128": "icons/icon128.png",
+    "16": "icons/icon16.png",
+    "32": "icons/icon32.png",
+    "48": "icons/icon48.png"
+  },
+  "manifest_version": 2,
+  "name": "Xget Now",
   "permissions": [
     "downloads",
     "storage",
@@ -86,19 +91,6 @@
     "https://arxiv.org/*",
     "https://f-droid.org/*"
   ],
-  "icons": {
-    "16": "icons/icon16.png",
-    "32": "icons/icon32.png",
-    "48": "icons/icon48.png",
-    "128": "icons/icon128.png"
-  },
-  "web_accessible_resources": [
-    "icons/*"
-  ],
-  "browser_specific_settings": {
-    "gecko": {
-      "id": "i@xi-xu.me",
-      "strict_min_version": "109.0"
-    }
-  }
-}
+  "version": "2.0.4",
+  "web_accessible_resources": ["icons/*"]
+}