Can you access the Add-ons site directly?

• https://addons.mozilla.org/firefox/extensions/

Do you still have extensions installed?

• Firefox menu button/Tools > Add-ons > Extensions

Yes, i can open that page directly. I thought I had a couple of extensions still but it does not show any now, the extensions page is just blank. Not sure whether I previously removed them all or whether this is another bug...

update: have just installed an add on from the direct webpage and it does NOT show under "extensions"

It is possible that there is a problem with files in the profile folder that store the extensions registry.

Delete the extensions.* files (e.g. extensions.json, extensions.ini, extensions.sqlite) 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 menu button/Tools > Add-ons > Extensions" then click the Tools button at the left end of the Search bar to check if there is a compatibility update available.

If this didn't help then delete addons.json and possibly prefs.js in case there is a problem with preferences.

Ha! I deleted extensions.json and "extensions-compatability" and now it's working! :)

Thanks heaps!!!