The Mozilla Firefox people in their forums (
http://forums.mozillazine.org/viewforum.php?f=49) offer step 1 as:
Clear your cache. Tools --> Options --> Advanced --> Network, Clear Now button.
If you are still having problems delete any cookies that have to do with the site. Tools --> Options --> Privacy, Show Cookies button.
If that doesn't do it, run these steps:
Go to Help, About to see your FF version and check for updates. 3.5.3 is the latest.
Go here to check/upgrade your Flash version:
http://kb2.adobe.com/cps/155/tn_15507.html
See if FF behaves with no add-ons loaded:
Start, Programs, Mozilla Firefox, Mozilla Firefox (Safe Mode)
If still no luck, tell us about your system:
Click Start, Run and in the box enter:
msinfo32
Click OK, and when the System Summary info appears, click Edit, Select All, Copy and then paste
back here.
There will be some personal information (like System Name and User Name), and whatever appears to
be private information to you, just delete from the pasted information.