Rated 4 out of 5 stars
Sometimes something breaks and proxy choose option constantly asks for verification code and doesn't proceed regardless the code is correct or not. Reinstalling helps whough.
UPD: Sorry, forgot to mention, it's firefox 57.0b5.
Thanks for your report. We will check it... it's very strange that addon keeps caching capcha image as we tried to make URL random and it should not be cached for sure. It could be some issue with Firefox itself as FF56 is experimental. We will check everything again from our end.