Create a new profile as a test to check if your current profile is causing the problems. See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

Profile Backup and Restore

• http://kb.mozillazine.org/Profile_backup
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

It is possible that there is a problem with the file(s) that store the extensions registry.

Delete the extensions.* files (e.g. extensions.sqlite, extensions.ini) and compatibility.ini in the Firefox profile folder to reset the extensions registry.

• https://support.mozilla.org/kb/Profiles

New files will be created when required.

See "Corrupt extension files":

• http://kb.mozillazine.org/Unable_to_install_themes_or_extensions
• https://support.mozilla.org/kb/Unable+to+install+add-ons

If you see disabled or not compatible extensions in "Firefox/Tools > Add-ons > Extensions" then click the Tools button at the left end side of the Search Bar to check if there is a compatibility update available.

If this hasn't helped then also delete the addons.sqlite file.

Sorry for long delay in replying.

I initially felt that, as a relative novice, the solution was more difficult to implement than living with the problem.

I therefore did nothing but the problem now seems to have righted itself.

Thanks for your help and both suggested cures.

Keith Carpenter

Hello,

I am glad to hear that your problem has been resolved.

If you have not already, please mark this thread as solved by marking the solution.
This will help other users experiencing similar problems find help faster and more efficiently.

I hope you continue using our products and thank you for contacting Mozilla Support.

Problem now regarded as solved

Keith Carpenter