Rated 5 out of 5 stars
The extension works great. I've been using it forever (before the current betas, I used to slightly mod the windows version).
Now, I'd be happy to make a small donation to the project if you could update the add-on to include MacOS native looking buttons - I could even provide the image files for it - even though is not exactly the point of it.
Extension signing broke my modding habits. :(
Since there are a few requests to add "better" support for MacOSX, I experimented with some code for navigation toolbar buttons.
Next CTB beta will replace the currently broken "simple" navigation toolbar button style with default toolbar buttons style Firefox offers for "hovered" state on MacOS.
"Old" MacOS buttons where atually fixed button images, while creating button shapes now is done by css code to keep better compatibility between Firefox versions and to save space. Not sure, if fixed images would still work the way they did, but as you said, this might be a feature for another add-on.