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

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox

You might try the following, the first part is to determine if an extension is responsible, but simply starting in Safe Mode, and then restarting normally has been seen to fix this problem.

1. "Alt+H" (help) > "Restart with add-ons disabled"
2. Once in safe mode test to see if back/forward work properly, make a note of if it works or not.
3. Restart Firefox, see if back/forward work properly, if they do the probably is apparently fixed for now.

Since you don't seem to have the "McAfee Site Advisor" extension which also shows up in plug-ins, I would try the solution for a corrupt localstore.rdf

• http://kb.mozillazine.org/Corrupt_localstore.rdf

For those that do have "McAfee Site Advisor", although the above appears to work, it would be better uninstall from system and reinstall

• https://support.mozilla.com/questions/876508

If the none of the above solutions worked, but it did work in safe mode, then try to find the extension at fault, see

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Extension_issues

Please mark "Solved" one answer that will best help others with a similar problem -- hope this was it. Would appreciate feedback as to your actual solution used, which extension if any was identified in your solution.