Are you talking about Firefox or Thunderbird? Firefox is only a web browser. It has no control of your mail. Many site issues can be caused by corrupt cookies or cache. * Clear the Cache and * Remove Cookies '''Warning ! ! ''' This will log you out of sites you're logged in to. You may also lose any settings for that website. Type '''about:preferences'''<enter> in the address bar. * '''Cookies; ''' Select '''Privacy. ''' Under '''History, ''' select Firefox will '''Use Custom Settings. ''' Press the button on the right side called '''Show Cookies. ''' Use the search bar to look for the site. Note; There may be more than one entry. Remove '''All''' of them. * '''Cache; ''' Select '''Advanced > Network. ''' Across from '''Cached Web Content, ''' Press '''Clear Now. ''' If there is still a problem, '''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Start Firefox in Safe Mode]''' {web link} A small dialog should appear. Click '''Start In Safe Mode''' (not Refresh). While you are in safe mode; Type '''about:preferences#advanced'''<enter> in the address bar. Under '''Advanced, ''' Select '''General. ''' Look for and turn off '''Use Hardware Acceleration. ''' Then restart. Poke around safe websites. Are there any problems?