You have to put at least one button in a custom toolbar to get it to stay. It will disappear if there are no buttons in it.

You can check for problems with the localstore.rdf file.

• http://kb.mozillazine.org/Corrupt_localstore.rdf

I know i have to put buttons on the custom toolbar but it disappear even if i do so. It's probably a conflict with some of the other installed addons.

Did you try to delete the localstore.rdf file?

• http://kb.mozillazine.org/localstore.rdf

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Yes, i tried with a new localstore.rdf file but this didn't help.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Which security software (firewall, anti-virus) do you have?

Some security software has virtualization or sandbox features that may cause problems by protecting and restoring files in the Firefox profile folder.

It seems that there is conflict with the Browser Backgrounds addon. When i disable addon the custom toolbar doesn't disappear. I like this addon but i guess i have to disable it if i want to use custom toolbar.