Hi, I do not know why your hard drive fills up. Not enough info. You could try this please : Go the 3 Bar Menu then Options --> General --> Performance and untick everything. change the recommended size lower then see how it runs. Note: 1 = No Multiprocessor = slow again. Try 2 Restart Firefox after making these changes please. Note : Acceleration is for your Video Card, monitor to see if need to turn back on. Suggest give your self a malware scan for any Bitcoin Miners or other things that could cause this, Please use more than 1 scanner as each uses diff tech : *https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware Save your Report and google each before deleting anything as do not want to delete something you need, If need help : *https://forums.malwarebytes.com/topic/9573-im-infected-what-do-i-do-now/ Post in only 1 forum, then wait. Also could try uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do : *https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles *https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer Reinstall with Current Release Firefox 58.0.2 with a Full Version Installer *https://www.mozilla.org/firefox/all/ Please let us know if this solved your issue or if need further assistance