It reflects on the abysmal quality of Adobe's software
and their QA. [...] I hope the people responsible for
this disaster, their managers and the QA team were fired.
Eh, I can kind of see how it might happen myself. Remember that time Valve had a bug in Steam for Linux that would wipe the user's hard drive? [1]It's easy to imagine how this sort of thing would happen - manual test guys don't have hidden folders in their root directories because their boxes are locked down by corporate IT and they can't create any folders in the root directory. Developers don't have them because they understand the unix way and know they shouldn't be putting files there. CI servers don't have such folders because, well, why would they? None of the test environments include the specific condition needed to trigger this bug - a hidden folder in the root directory - so the bug never appears in testing.
Is it bad and serious? Absolutely. But I don't think the fact testing missed this is a sign of testing incompetence - you could have cutting edge testing following every industry best practice and still miss this bug.
[1] https://github.com/ValveSoftware/steam-for-linux/issues/3671