Mozilla is unhappy because the use of browser engines other than WebKit will be restricted to the EU, forcing them to develop two different apps.
For an independent browser like Firefox, managing two browsers is not easy, so it can be forgiven that this could be seen as almost harassment.
Also, the fact that the use of browser engines other than WebKit is limited to iOS means that the use of WebKit is still forced on iPadOS, which also increases the effort for Mozilla.
Such a weird take.
Also this has nothing to do with programmers.
Just saying their OS sucks, bad designs, buggy UIs, etc. They don’t even decent software, and I already saw many stupid bugs.