I'm unsure what is restoring the data at this point.
Can we just rule out it is not firefox.exe in memory making the restoration.
Run a quick scan and when it has finished (before taking any further action) please evoke task manager (CTRL+ALT+Delete) and terminate any instances of firefox.exe that are loaded.
Next click on the quarantine all button.
No reboot message will be generated as this is a file edit and not a removal but please next close Malwarewarebytes and then reboot the the computer.
Please rescan and verify whether the detections persist.
Thanks for your help on this.