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

Type about:support in the address bar and press enter.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Delete the extensions.* files (e.g. extensions.json, 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.

After, restart Firefox.

See "Corrupt extension files":

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

You will have to approve the updating one last time.

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Thanks for the speedy response. I deleted the files you mentioned after closing firefox, then started it up again. All the tabs were there again. The 'unable to install addons' articles don't address the problem as I can install them, and they work, but when I close ff and open it again they ask to be installed again. There are no yellow boxes saying I've got installation turned off or anything. Also, it's not just a few but everything. So probably unlikely to be a compatibility issue. Plus as I said they do work just not after a restart. I think I will have to stop using firefox as it's just too annoying! Thanks anyway!

Did you check out the how-to-fix-preferences-wont-save section?

Are the websites listed in the customized homepage: Wrong home page opens when I start Firefox - How to fix