great theme. using it on KDE (Kubuntu) and it matches the "Arc Dark" plasma theme perfectly. it's just like the "Arc Dark" theme by tofuHero but the active tab is highlighted with a blue bar (like in the photo). also, the foreground (font) color of background tabs is a tad more subdued.

here's the link to tofuHero's theme for reference:

https://addons.mozilla.org/en-US/firefox/addon/arc-dark/