Use the latest version of another browser. For more information, see the article Switch to Firefox Extended Support Release (ESR) for personal use. Firefox ESR does not come with the latest features but it does have the latest security and stability fixes. Firefox Extended Support Release (ESR) is an official version of Firefox developed for large organizations, such as universities and businesses, but it can also be used for personal computers.
Install Firefox Extended Support Release.
Instead of downgrading to an older, insecure version of Firefox and changing your update settings, you should consider these alternatives: In the General panel, go to the Firefox Updates section. Click the menu button and select Settings. Click the menu button and select Options Preferences. In the Menu bar at the top of the screen, click Firefox and select Preferences. To prevent Firefox from automatically updating itself after you install an older version, you'll need to change your Firefox update settings:
For example, uBlock Origin has its source code on GitHub and it is actively developed by many contributors. The extension must be open source and you can get the source code on GitHub or somewhere else.The extension must be "recommended" by Mozilla, which means it has been audited for security and privacy by Mozilla engineers.The following guidelines can keep you away from bad extensions: Mozilla has banned nearly 200 malicious Firefox add-ons over the last two weeks.Web Security Firefox Add-on is Secretly Collecting User’s Browser History.'Web Of Trust' Browser Add-On Caught Selling Users' Data - Uninstall It Now.You should not install extensions or themes without knowing who the author is and whether the code has been hijacked. Even some "featured" extensions are proven to be malware. Mozilla is NOT responsible for security auditing of extensions at which gives malware chances.