Step # 5 is a browser refresh, which will create a new user profile and remove your browser extensions without deleting other items like your bookmarks, passwords, browsing history, cookies, etc. A clean reinstall of the Firefox software will not remove your Firefox user profile that is stored a hidden folder at C:\Users\\AppData\Local\Mozilla\Firefox\Profiles\ so none of your browser extensions, bookmarks, etc. Use a fresh copy of the ESR v52.9.0 installer from Directory Listing: /pub/firefox/releases/52.9.0esr/win32/ (choose the subfolder for your region and language e.g., the /en-US subfolder for the English-US installer Firefox Setup 52.9.0esr.exe). If you antivirus doesn't detect anything run a second-opinion on demand scan with Malwarebytes Free v3.5.1 (the legacy version for Win XP and Vista, download from the FAQ article or from ) to look for any malware or PUPs that might have been missed by your antivirus.Ī clean reinstall of Firefox as instructed in STEP # 4 should solve the problem if your Firefox installation is corrupted. I would actually start with the final step in that support article and scan for malware, just in case your browser has been infected with a cryptojacker that is using your computing resources to mine Bitcoin or some other cryptocurrency.
Try following each of the steps listed in the support article Troubleshoot and Diagnose Firefox Problems.