Try the Firefox Safe Mode to see how it works there. The Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• You can open the Firefox 4.0+ Safe Mode by holding the Shift key when you use the Firefox desktop or Start menu shortcut.
• Or use the Help menu item and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Don't select anything right now, just use "'Start in Safe Mode" To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut (without the Shift key) to open it again. If it is good in the Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one.

Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.

Tried this - disable all addons - still does not work correctly.

Try clearing the cache! I'd upgraded tinymce, and it was broken. Cache clear worked for me. Options->Advanced->Network->Cached Web Content-->[Clear Now].

Also I noticed that FF18 was insisting on using an old expired certificate on a website using SSL and it would not let me on the site. I cleared the cache and it then got the new certificate and was good to go. I'm not sure certificates should ever be cached.