If you cannot customize Firefox navigation bar, add new icons etc
It is rare, but it may happen; Firefox opens with a navigation bar that refuses to be customized, not letting you add icons, the search bar, nothing! If you uninstall and install again Firefox, the problem remains. If you disable even all of your extensions, the problem remains, the navigation (address) bar refuses any customization whatever!
The only solution that worked in my case was to enter my Firefox Profile (at :\ Users \ YourWindowsUserName \ AppData \ Roaming \ Mozilla \ Firefox \ Profiles \ YourFirefoxProfile). I copied the whole profile folder to a safe location in case I needed to restore it, then I pressed F3 and searched for rdf files. I found a lot (such as install.rdf, localstore.rdf, mimeTypes.rdf, etc), I deleted all of them and restarted Firefox.
The problem was solved at last, I was able to add to the navigation bar the search bar and all the icons I want at the top. The only side-effect was that some extensions lost their configuration and LastPass was missing entirely.
I searched the copy of the old profile folder and found inside it the lastpass folder. I copied that to the new profile location and lastpass was installed again, remembering all of my sites and password data!
If you are thinking of trying this solution, just don’t forget to copy your profile to your Desktop or elsewhere, so that nothing is lost and all changes can be undone. Then zip it and store it somewhere in your documents to make sure, after some time passes, that you really don’t need to keep it anymore.