WebExtensions: web_extension_content_script_build() calls WebKitGTK from a thread
It calls webkit_user_script_new_for_world()
from a thread. This is unsupported and asserts with a debug build of WebKitGTK.
It calls webkit_user_script_new_for_world()
from a thread. This is unsupported and asserts with a debug build of WebKitGTK.