hb I use it all the time too.
As I said/implied…
It is only since the most recent update of Firefox and it doesn't happen with IE (I haven't tested with Chrome but I guess that would work ok too). It is Firefox that is the problem not Google Translate per se.
It (failure to paste or rather failure to copy correctly to the clipboard) is a known problem as per the Firefox forum and, as I said, as well as failing to paste in (or, strictly, failing to copy to) other applications it causes Achat to crash.
It only happens if you marquee select the translated text and Ctl-C to copy releasing the keys immediately. If you delay the release a couple of seconds it works fine.