I checked again, uninstalled FoxyTab, reinstalled, restarted, nothing, the Copy URL functions just don’t work here. Again: FF 56 32 bit, FT 2.7, under Win 7 64 bit.
Is it possible to install 2.5 again, to test?
Edit: I’ve tried 2.5, I’ve deactivated all extensions but FT, I’ve used the restorer in about:Firefox, and nothing. Result: not only any copy to clipboard function from FT doesn’t work; also window size and position is not restored, plus FoxyLink doesn’t even show the menu as if it’s not installed. So I guess my Firefox installation is fubar, I’ll have to remove everything and start anew, hopefully making everything work again.