I used this theme for a few years - it's a great looking and nostalgic theme. However, it's pretty old now (the last release was in 2019), and as a result it doesn't have good compatibility with the new Firefox UI. The "Customise Toolbar" page is broken, displaying invisible white text on a white background. Also, several UI elements are not re-themed, remaining the default light or dark colour.

As much as I like this theme, I've had a better experience with other themes recently, and I think you will too (unless this theme is updated in the future).

not well fit
to wide screen