Wow, thanks. It seems that web clipper 6.13 just can't work with "some" websites due to a compatibility problem. I'll try 6.9.3, and hope for a harmony between these two guys: EN and FF.
As described in the title, web clipper does not work with firefox quantum 57.0. When I tried to clip the webpage, only a gray rectangle showed at the top-right cornor in firefox, there's nothing more I could, no button, no user interface. Please fix this! Thanks!