Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

• https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

FF5 homepage, scroll bar and browser back/forward page buttons don't work, and don't light up on mouse-over or respond to clicking:

"AVG Safe Search" extension seems like a possible match -- disable it, you can't run Firefox with with the extension. Disabling is only a temporary solution you should reinstall "AVG Free" without the Link Scanner Component per instructions in Problematic extensions referencing Grisoft's help pages. If this extension is enabled a question would be how it got enabled as it is on the Blocklist and has been a problem going back to Firefox 2. What is amazing it that not everyone gets hit with it at the same time.

• Problematic extensions - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Problematic_extensions
• Blocked Add-ons :: Add-ons for Firefox
  https://addons.mozilla.org/en-US/firefox/blocked/
• Extensions.blocklist.url - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Extensions.blocklist.url
• Extensions.blocklist.enabled - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Extensions.blocklist.enabled
• Firefox sometimes crashes when searching normal images on Google image. | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/questions/761439

Cor-el, dmcrichrtchie thanks for your suggestions. I'll follow them and post a reply.

I disabled the link scanner component in the free version of AVG I'm using but it didn't solve the FF5 problems I posted on: The back/forward, scroll bar, homepage and I can't open the FF5 all-in-one sidebar add-on I installed (forgot to mention this one!).

I'll try restarting FF5 in safe mode Firefox later today to check if any extensions are causing the problems.

Thanks again for your suggestions.

Oops, sorry - double post!