That's pretty extreme. Mozilla does not have an agreement with Yahoo now uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. 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 57.0.2 with a Full Version Installer https://www.mozilla.org/firefox/all/ Below is to have on hand if issues, 1st is to check, 2nd to monitor if need it. So the 2nd is to do this please : go to the Firefox 3 Bar Menu --> Options --> Privacy & Security panel and under Permissions check (put a tick in the box) the setting to Prevent Accessibility Services from accessing your browser. Monitor in Task Manager. Should stay below 2 gigs. If excessive then do below and monitor and change if need to...Test and go up again , go back down, it will eventually get a zone you and it can live with. 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. It may have gotten into your Profile so if has : Please make a new Profile and test : https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles Come back if need help with the profile. fyi : https://www.howtogeek.com/334716/how-to-customize-firefoxs-user-interface-with-userchrome.css/ Please let us know if this solved your issue or if need further assistance.