Is this still maintained?

[R0dri]

Looks like it isn't when I try to install to safari.

[Haroenv]

The Safari extension isn't maintained anymore indeed, since you now need to make a cocoa app to make a safari extension, which we haven't done yet since nobody asked for it.

The extension itself is open source, so if you're interested in adapting the current code to make it work in newer Safari, PRs definitely welcome!