Have a look at

• preferences are not saved

Please post back again after you have read that article and tried to follow its advice.

I have read the article. Nothing applies to my case. When I click OK in the Options window, the changes are saved, only the window doesn't close, I have to close it by clicking the "X".

Sorry if that is what happens I do not know the answer. As long as it is making the changes i suppose it is only a minor inconvenience. Maybe someone else will be able to give you an answer.

Thanks John for trying to help anyways. Yes, it is a minor inconvenience only but still there :)

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

Well, thank you, cor-el, starting in Safe Mode removed the problem! Now the long work begins - finding out which add-on is causing it...

Tip disable addons half the list at a time rather than one by one, if you have quite a few. Then try the other half if necessary, and split that or the original in half again.

I figured it out, it wasn't just one add-on, it was a few causing it.

Can you tell us which extensions were involved?

It helps others who read this thread.

What then caused your problems, others may well have the same combination, and a similar problem.

HP Smart Web Printing 4.51, Noia 4 (five themes in one) 1.5.4, and Noia 4 Theme Configurator are the ones that caused problems in my case.

Thanks for the reply.