You can try to reset this pref via the right-click context menu to the default value.

• browser.uiCustomization.state

You can create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Man, i don't understand a word of what you say/write. where the hell is: browser.uiCustomization.state

and for heaven's sake, why should i go through all the setting up a new profile hassle - in the morn the bar was there, i updated it and the address bar is swallowing all of it - it's a glitch on your end. Sorry - your piece of advice is absolutely useless - i have just checked the 'create a new profile' option and it's so bloody complicated that i will never go through all this. you know, i am not a computer geek like you.

"If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems." - how the hell do i do that?

Can't you just do something about Firefox - it's been a source of constant trouble since the beginning of summer 2017

Mind you I did nothing to my profile. I simply udpated Firefox to the latest version

be cautious not to copy corrupted files to avoid carrying over problems. - and how do i know which files are corrupted and which are not??????????

In the Firefox Menu select "Help -> Troubleshooting Information" and click "Open Containing Folder" (see note below) - nothing of the kind happens - not OPEN CONTAINGIN FOLDER appears, it's all a load of bollocks

I'm not having any problems with the two profiles I use with the beta versions. In both I still have the search bar.

Does the new profile work?

Did you try Safe Mode in the original profile?

• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can only find out what file(s) are causing problems by trying to copy the file and check if the profile still works properly. Copying SQLite databases and other files (passwords) that have nothing to do with toolbars should be OK. Copying files like xulstore.json and prefs.js is best avoided.

I'm curious why you use a beta/test version when you aren't very experienced to deal with (minor) issues you can encounter with test versions.

Also make sure in case you use more than one Firefox version to use each Firefox version with its own profile and not use the same profile with different Firefox versions. Switching a profile between versions can easily corrupt a profile.

Note that you can use the about:profiles page to create a new profile. You can open "about:" pages via the location/address bar

• "about:" is a protocol to access special pages

I switched to the beta version at some point a while ago when the regular version was causing more problems than providing advantages

As a starting point, you could try the "Restore Defaults" button on the Customize pane. It's at the bottom. See: Customize Firefox controls, buttons and toolbars. Normally that would put the search bar back onto the toolbar next to the address bar, or it might show up in the Customize panel among unused controls you can add back.

I notice someone else mentioned the same problem with the latest beta: Search box won't show in the UI.