move the jigsaw piece menu back to the hamburger menu for small resolutions?

From https://fosstodon.org/@m0xee@librem.one/113485526573735455:

I wish someone could find a way to move the jigsaw piece menu back to the hamburger menu, where it should be — I could use this even on desktop with more screen real estate. I know that this was done for compatibility with manifestv3, blah-blah-blah — but I don't need this extension menu that often to justify wasting screen space on it, I probably would like an icon for uBO there — but not this jigsaw thing 😩

I agree, it would be nice if the jigsaw piece menu would not take up space there, if the screen width is low (-> mobile phone in portrait mode).

@dannycolin: maybe it is possible to solve this nicely upstream in Firefox, what do you think?