Many site issues can be caused by corrupt cookies or cache. * Clear the Cache and * Remove Cookies<br> '''''Warning ! ! '' This will log you out of sites you're logged in to.''' 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'''. Poke around safe websites. Are there any problems? Then restart.

Can you attach a screenshot? *https://en.wikipedia.org/wiki/Screenshot *https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem *Use a compressed image type like PNG or JPG to save the screenshot *Make sure that you do not exceed the maximum size of 1 MB See also: *https://support.mozilla.org/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER