As others have said, whatever was done in the recent update has messed up everything. I can't even view emails or use Google properly with the add-on enabled. Please fix this! It used to be great :(

*Edit* The fix for this issue seems to be removing then re-adding the extension. Everything is working as it should again so I changed my review to 5 stars as the problem seems to have been caused by the recent Firefox update and is not the developer's fault.