That's really bad. Deleting user data is one of the most loud ways to declare that "we're bad at software development!" I guess I should consider trying Ungoogled Chromium or maybe Pale Moon. I worry the former will be a menace to build because I don't have lots of RAM and CPU. Edit: I don't use the feature but still...
They will remove the data in a future release. I.e. if you don't read the entire release notes for all the software you use, there's a chance that your data will be removed inadvertently, if you happen to use the feature.
Firefox has problems with data loss. I have lost my open tabs on multiple occasions in scenarios where it's totally possible to recover the entire data (just using atomic writes). Recently, I mistakenly opened FF 52 instead of FF 61 (Debian has 52), and all my bookmarks were deleted. Luckily I had a backup of the user profile so that I survived that. I like FF, but I cannot trust it with my data one bit. And now it's no more only mistakes but it's intentional, user-hostile design decisions.
