Breeze style tabs for Firefox

Recently I was struggling to make tab close icons look closer to Breeze theme. Now I managed to make tabs look Breeze-ish too! The icon rules are also better now, opacity works without superposition problems:

Firefox tabs a-la Breeze

Firefox tabs a-la Breeze - circular icon

The userChrome.css is very messy and probably redundant, but hey, it works. The element rules were changing quite a bit with every new version, so I’ve cleaned up the old stuff. Here’s the code I’m running on Firefox 60.0.1:

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