Wow, this is brilliant! Works really well with Dark Reader too.

It changes the experience so much and makes it look like I am in the software.

Changes all tabs to be the same colour, I had hoped they'd be different colours, to match their web-page, maiking it easier at a glance to click on the tab I was looking for. Otherwise works well enough, though I do think UX design is worsened by the inability to tell where the content starts and the toolbar ends.

This add-on breaks all other themes, so it's not good. All it needs to do is change the tint of the tabs and leave everything else alone, but it can't do that.

works seamlessly and smoothly with any website. also has a bunch of customization options that allow you to really make Firefox yours :)