Did your downloaded file contain the word "stub"? That installer connects back to Mozilla for additional files, which may be blocked on some systems. Could you try using the "full" or "offline" installer? On the following page, scroll down to your preferred language: https://www.mozilla.org/firefox/all/ '''For maximum plugin compatibility, choose the 32-bit version.''' ---- Now... it's also possible that you have or had a malware infection that is affecting your use of your system and changing system settings. If you haven't swept for malware, please supplement your regular security software with the free scanning/cleaning tools listed in our support article: [[Troubleshoot Firefox issues caused by malware]]. If Windows won't let you run those, either, it might be time to head over to a specialized malware cleanup forum for expert assistance. The support article lists a few choices along those lines.