Oh, finally I figure out what are you talking about.
I tried to install "clear dark Facebook" using the Stylish extension, while the "install" process never starts after clicking.
So I then tried "install style as userscript", the install succeed, while no change for the facebook theme. And it popped up the warning saying @grant issue.
I'm wondering how can Maxthon help in this case with the info provided that the author had so solution either?