Bug 1930776 Implement userScripts.execute (#29811)

Bug 1930776 Implement userScripts.execute

Author: rebloor

webextensions/api/userScripts.json

@@ -210,8 +210,7 @@
               },
               "edge": "mirror",
               "firefox": {
-                "version_added": false,
-                "impl_url": "https://bugzil.la/1930776"
+                "version_added": "153"
               },
               "firefox_android": "mirror",
               "opera": "mirror",