When we open up Firefox we get a pop-up that says in the upper left "Your PC's Performance is Poor" and in the box below that it says (after a little warning sign) Fix Windows Errors Immediately! and then a button to click for "Download Repair Tool". We can't seem to get rid of it. We have run a Norton Quick Scan & Full Scan and a scan using Malwarebytes, which none of it detected any problems.
The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information.
Note: This will cause you to lose any Extensions, Open websites, and some Preferences.
To Reset Firefox do the following:
Go to Firefox > Help > Troubleshooting Information.
Click the "Reset Firefox" button.
Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
Firefox will open with all factory defaults applied.