What's your computer system and Firefox version?

It's possible that the Firefox window is opening outside where you can see it. Try this; Open Firefox. After it opens, wait a few moments. Then mouse to the Firefox icon, right-click and select Open New Window. If this works, close the first icon.

I've tried that several times and will not even open new window. I'm considering a restore on my PC since it's only 2 mouths old and I have everything backed up.

It could be a Firefox issue or there are some virus/malware that causes it to not close and keep running.

Could try this just to make sure : 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.

Then

Please : https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer and https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles then https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Note: Any customization will revert back to default, you will also need to reinstall Extensions.

Please let us know if this solved your issue or if need further assistance.

I found two different versions of Firefox on my PC. I was able to uninstall one version then the other that I was trying to uninstall earlier then reinstall Firefox.