I've love this addon. There are some weird issues since the Firefox 89 update though.

The standard "System theme" is supposed to "Follow the operating system setting for buttons, menus, and windows" yet in Firefox 89 it no longer does so. This extension lets me at least manually set Firefox colours to match the OS theme, and visually differentiate between active and inactive Firefox windows.

Useful but the display "pop up" window covers the saved themes tab and prevents you from selecting previously saved themes.

Not 5 stars because it needs improvement, further development, and repair. Setting (Background Tab Text Color) to black changes the colors of the Back-button (I have disabled Proton theme). I had to use a CSS-code to get the Back-button to display the colors I want.

Can't get to page to change anything so at this point, totally useless.

It's straightforward to use. You can, in real-time, customise the colours of Firefox. It's faster than having to sift through the ugly themes available elsewhere.

Like some of the others, the page does not load for me. So for the moment, useless.

Edit: I don't know why, but I tried loading the page from a different country via a proxy changer and it finally worked. It now also works without the proxy. So if you're having the same problem as I had, try a proxy/VPN server switch.

The new Firefox broke Firefox color, there's a white horizontal line below my tabs, above my address bar, for all dark skinned themes.
I had to manually go fix this by turning on a dark color from "Advanced Color --> ToolBar Top Separator"

Not very configurable, and the colour picker is extremely primitive.

The writting in the bar uptop are WAY too small ... put some other choices like nature selection and NOT those flashy color that make your head spin ... thank you

I like the feature, and it's fun to use. However, it's not clear how to make the theme active. It doesn't appear in the list of themes in settings, and clicking on it in the page where I saved it does nothing. Saving and using should be intuitive, and the theme should show up in settings for ease of use.