It seems there's only a small overlap between the people suffering and the people being able to solve this.
If a "normal" web developer struggles with that, they can provide JavaScript workarounds, perhaps many, but they usually aren't that intimate with C/C++ and the whole framework on which Firefox is based.
Also, as with most projects, if a webdev can solve this problem with a workaround now, they don't invest time to provide a proper long-term solution. If if they are capable of improving Firefox, they'd still need to create the JS workaround, because short-term is what they are paid for.
If a "normal" web developer struggles with that, they can provide JavaScript workarounds, perhaps many, but they usually aren't that intimate with C/C++ and the whole framework on which Firefox is based.
Also, as with most projects, if a webdev can solve this problem with a workaround now, they don't invest time to provide a proper long-term solution. If if they are capable of improving Firefox, they'd still need to create the JS workaround, because short-term is what they are paid for.