I think you are going to Options / Privacy and unchecking the box for suggesting bookmarks in the Location bar, as described in this article: Address bar autocomplete suggestions in Firefox -- "How can I control what results the location bar shows me?" section.

That change definitely should be remembered from session to session. This article lists possible explanations for not retaining settings between Firefox sessions: How to fix preferences that won't save. Does anything there help? Note: if you have patience for troubleshooting, skip the Refresh until you've checked the other things.

Thanks for your suggestion, I allways "untick" the privacy boxes but it never saves my result... I will read the last article you reffering to and hope I can find a fix.