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.

I do not have any programs like that installed. The only setting that will not persist is the spell check context menu setting. I have followed the guide to no avail and there is no user.js file present in my profile folder. So really stuck now. Can i force the setting by editing a config somewhere?

Hello vermillion,

You could check layout.spellcheckDefault on the "about:config" page - see :

http://kb.mozillazine.org/Layout.spellcheckDefault

Do you have a dictionary installed  ?

If not, you could chose one in your preferred language :

https://addons.mozilla.org/en-US/firefox/language-tools/

The dictionary is installed and working correctly. It is just that the setting to use the spell check in the context menu turns off after exiting Firefox, so has to be enabled once Firefox is launched each time.

Did you also verify that the Firefox program folder is empty and gone after uninstalling Firefox to do a clean reinstall?

I think the problem is me. I always tested by opening Firefox and right clicking in the homepage search bar, spellcheck is not checked. On answering this post i right clicked in this text box and the spellcheck is checked. So this must be a feature of the British English Dictionary by Marco Pinto.

Interesting.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.