There's a bug report about it with lots of duplicates and 71 votes. I use Ctrl+W to close tabs, so losing work in other tabs is just one key away. For me, it isn't nitpicky.
> having a flashier UI would address and (potentially) attract more users.
You don't know that though. You think it will attract more users.
You'll need some kind of metric to know what people really want. "Gets often repeated in discussions" is one, "which bug reports get voted on" is another.
I think alt-f4 closes the window while ctrl-q closes down Firefox entirely (in my KDE setup at least.)
On Windows ctrl-q doesn't work for me though.
As for why I sometimes use it it is because I can then do a restore session after restarting Firefox and get back everything.
(On Windows I have to find the now hidden menu and select Quit Firefox or something like that.)
I definitely think that this should be handled by the OS though.
[1] https://addons.mozilla.org/en-US/firefox/addon/disable-ctrl-...
Then there are the asian and middle east that do not even use the same alphabet. Though those may use the QWERTY as an underlying layout for compatibility.
> * Way too easy to quit the whole browser with Ctrl+Q (Chrome uses Ctrl+Shift+Q)
Saying that it's nitpicky to include this in your list would be huge understatement, it's straight out ridiculous. I have always found Firefox to be more responsive and less resource heavy than Chrome, so I don't know why you had problems with that.
But yes, you are right when you imply that Firefox seems to have prioritization problems, lots of them imo. However, it is understandable to me, making the UI looking prettier is for marketing, not usability. Most of these things you listed are not addressing a lot of users, on the other hand, having a flashier UI would address and (potentially) attract more users. But their management still needs to improve, and as a company, they should have better direction.