Comment # 2 on bug 1191415 from Luciano Santos

(In reply to Fred Fu from comment #0)
> Flatpak firefox and firefox downloaded from firefox.com *do* have the same problem. 
> ...
> I am not sure whether this is an upstream bug.

Hi Fred,

It does sound like an upstream bug to me. Do you still experience this issue?

There's an old upstream bug [1], specifically to Windows, that looks somewhat
similar to this one and it's an interesting reading. At the bottom there's a
case of someone on Linux with a similar issue too.