hi, you might want to try a clean reinstall in this case:

• download the full firefox setup file from https://www.mozilla.org/firefox/all/
• uninstall firefox on the machine
• manually delete all remaining files in the firefox program folder, which usually resides in C:\Program Files (x86)\Mozilla Firefox\
• reinstall firefox

Hi!

did like you sugested. As soon I use my previous profile problem is back so the lock is somewhere within profile. I could give up the old profile but I have bookmarks there . On old times bookmarks were just one html file , nowdays not, so it is not that easy migtare just bookmarks :(

So where in the profile is the lock located?

by the way prefs.js in my profile has user_pref("browser.shell.checkDefaultBrowser", false); and there is no user.js file

What protection programs are you using?

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Do not have any of listed programs. Created new default profile, copied prefs.js and places.sqlite from old profile , now looks working, I have my bookmarks, homepage and about:config does not show locked prefs so far.

That was very good work. Well Done. Please flag your last post as Solved Problem so others will know.