This sounds like a Windows issue as you mention nothing about Firefox other than you have it installed.. Please check Windows forums for the answer :

• https://www.bleepingcomputer.com/forums/f/229/windows-10-support/
• https://www.tenforums.com/

You could try from a Dos prompt Right Click and Run as Administrator  : SFC /Scannow (SFC <space>/Scannow) command uses local files to fix issues does same thing but in Win 10 go Up and get New Files is better.

Can also : 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.

No idea what your going to do. If you made a Trouble Shooting Disk, boot from it. Go to a Friends and make one. Or a full version installer made by a ISO file. You would need to just bypass installing and just use it to get windows up so can work on it. This tool will work to make a Bootable disk. DO NOT INSTALL.

• https://www.microsoft.com/en-ca/software-download/windows10

• Thank You for contacting Mozilla Support.

Hi  !

Would you please check your Windows Settings => Desktop  ?

Something may have changed with the last Windows update.

If that's not it, maybe you could post a question on the Microsoft support forum :

https://answers.microsoft.com/windows

Good luck  !

Hi, maybe something to do with Windows Task View.

If the button is missing on your Taskbar, right click it > Show Task View button.