Hi, hold down the Shift key when you start Firefox to start in Safe Mode. More - [[Troubleshoot Firefox issues using Safe Mode]]. If it works in Safe Mode, disable any theme or extensions you have - 3-bar menu > Add-ons > Themes/Extensions, then restart Firefox; now if it's still OK, re-enable them one by one until you find the culprit. You may need to restart Firefox after enabling some extensions. Note: If you use '''userChrome.css''' - you don't have it if you don't know what it is, this is also disabled in Safe Mode, so should be regarded as an additional suspect, and can be disabled to test by placing '''/*''' before, and '''*/''' after the file in the '''chrome''' folder, then restarting Firefox. ---------------- Disable any antivirus programs you are using. If it works, your AV may need updating. --------------- Try a Clean Reinstall; this means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location. With Firefox closed, use another browser to download Firefox from https://www.mozilla.org/firefox/all/ and save the file to somewhere convenient on your computer. Now delete the Firefox installation folder which should be in one of the following locations - C:\Program Files\Mozilla Firefox C:\Program Files (x86)\Mozilla Firefox You can now double click the file you previously downloaded to install Firefox. ----------------------- Try working through [[Firefox won't start - find solutions]] ''If your question is resolved by this or another answer, please help other users by marking the best reply as Solved. Thank you!''

Ok. Safemode didn't work and disabling AV didn't work