Hello Matanyao, This Firefox problem might be solved by performing a ''Clean reinstall''. This means you remove Firefox program files and then reinstall Firefox. Please follow these steps: #Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer. #After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu). #Delete the Firefox installation folder, which is located in one of these locations, by default: #*'''Windows:''' #**C:\Program Files\Mozilla Firefox #**C:\Program Files (x86)\Mozilla Firefox #Now, go ahead and reinstall Firefox: ##Double-click the downloaded installation file and go through the steps of the installation wizard. ##Once the wizard is finished, choose to directly open Firefox after clicking the Finish button. More information about reinstalling Firefox can be found [https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems?esab=a&s=troubleshooting&r=3&as=s#w_5-reinstall-firefox here]. <b>WARNING:</b> Do not run Firefox's uninstaller or use a third party remover as part of this process, because that could permanently delete your Firefox data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. <u>These cannot be recovered unless they have been backed up to an external device!</u> Please report back to see if this helped you! Thank you.

Are there any prefs on the <b>about:config</b> page that have Locked in the status column? You can click the Status heading to sort by this column. *http://kb.mozillazine.org/Preferences_not_saved