Are you still able to log in?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

If there is still a problem, Start Firefox in Safe Mode {web link}
by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh).
Did this help?

While you are in safe mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}

Dear Fred

I have logged on in Safe Mode but still have a problem. I can log onto Barclays Bank site but if I try and do something on the site I get a message that says "Your Browser sent a query this server could not understand" This has happened over the past month after many years of being OK. By logging on using Google Chrome there are no problems. Graham Richings

Bad Request Your browser sent a request that this server could not understand. Size of a request header field exceeds server limit

This issue can be caused by corrupted cookies

Remove History For One Site {web link}

Open the History Manager <Control> (Mac=<Command>) <Shift> H.
In the search bar, enter the name of the site. Right-click on one of the listings and select
Forget About This Site.
This should remove all information, including any site settings

If clearing cookies didn't help then it is possible that the cookies.sqlite file in the Firefox profile folder that stores the cookies got corrupted.

• rename/remove cookies.sqlite (cookies.sqlite.old) and when present delete cookies.sqlite-shm and cookies.sqlite-wal in the Firefox profile folder with Firefox closed in case cookies.sqlite got corrupted.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data