How do I find what avast did and prevent if from taking this action without me first confirming this is should be done?
In scan settings, exclude the folder.
Unfortunately, this explicitly means you trust Mozilla to not have any malware…
But one day the devs will work out that the regular patrols should have a report but do nothing setting, or better, a report and auto-submit for false positive analysis.
We can only hope.
Gordon.