Windows-10-Dark VS firefox-sweet-theme

This and this are pretty close I think.

I think this is the one

I've been using Linux since 2012, I started on Xubuntu 12.04, because Ubuntu was simple too bloated for me, but I must say, Xubuntu's default look didn't look great, it was better than Windows XP that's for sure, so I lived with it until I saw Windows 10's look and I fell in love with it, then I found this Windows 10 Dark theme for Linux and I've been using this theme ever since.

My Linux Mint Cinnamon using the Windows 10 Theme by B00merang-Project

I'm running Xubuntu 20.04 and I'm this dark theme: https://github.com/B00merang-Project/Windows-10-Dark/

If you want sweet theming this theme does it well https://github.com/EliverLara/firefox-sweet-theme

It's a rabbit hole that can keep you busy for a while, but the results can look beautiful

Sweet Dark Kvantum along with the Firefox userChrome (same dev) is straight 🔥

It's a feature so that you can drag the window easily if your tab bar is full. You can get rid of it by enabling the title bar, but that's even uglier imo, before - after. Another alternative is just using a theme with an entirely different layout, like firefox-sweet, not sure about this one specifically on windows tho.