Hello dear people of the internet!

Recently I noticed a buggy behavior in Ironfox (hardened Firefox Mull descendant) and tried to isolate it. It seemingly boiled down to a Firefox upstream issue, but now I'm not so sure anymore, as it does not apply to LineageOS, which I happened to use recently.

Anyway, this is what is happening, using GOS on a Pixel 7a and Ironfox since 134.x (it does not happen on 133.x, nor did it happen before around the time Mull ended, I think) :

Using Android's 3 button navigation (not applicable to gestures), when tapping on the address bar of Ironfox/Firefox, the keyboard opens as it expects a URL or search input.
When tapping the "down triangle" / rotated back button, it should only close the keyboard and possibly deactivate the input, i.e. closing the address bar.
Instead, it closes the keyboard, address bar, but also triggers an additional "back" input, going to the previous site or closing *fox entirely.
It essentially triggers a double back input.

I reported this on Bugzilla, but then I noticed the "correct" behavior on another phone on LineageOS using the same *fox versions.
It now seems isolated to GrapheneOS, since I managed to reduce any other factor, version or any other apps or input fields inside the browser.

So I'm seeking confirmation from other GOS users.

If you happen to use current versions of Ironfox or Firefox and maybe are even able to test this on ≤133.x, I'd very much appreciate it.
Please keep in mind that using Android's 3 button system navigation is a must. I could not produce the same behavior using gestures, that is swiping from the side.
It is not present on other apps or browsers like Vanadium.

Thank you very much in advance, have a nice day.

P.S. I mentioned *fox closing entirely, which I wanted to elaborate, since this is the most bothersome scenario:
Opening a private tab, you can not access bookmarks (or any other menu related function for that matter), without *fox completely backing out to the app launcher and needing an additional launch in order to access bookmarks or the menu, starting in a keyboard/input closed state.
This and always being forced to go back one site when having triggered the URL bar input are the only instances I experience this and seriously interrupt usage.