Hello,

Many site issues can be caused by corrupt cookies or cache. In order to try to fix these problems, the first step is to clear both cookies and the cache. Note: This will temporarily log you out of all sites you're logged in to. To clear cache and cookies do the following:

1. Click the menu button , choose History, and then Clear Recent History....
2. Under "Time range to clear", select "Everything".
3. Now, click the arrow next to Details to toggle the Details list active.
4. From the details list, check Cache and Cookies and uncheck everything else.
5. Now click the Clear now button.

Further information can be found in the Clear your cache, history and other personal information in Firefox article.

Did this fix your problems? Please report back to us!

Thank you.

Fix was to completely uninstall Firefox, delete all related folders and registry entries and reinstall. It shouldn't need to come to that, but...

We'll see how long it goes before happening again.

This wasn't a single site issue. It happens everywhere, so it would be unlikely to be cookies, although I had already done the obvious.