Extension looks good, thanks, but I think I am seeing a bug:

With 2 or more styles/themes installed for a site (any site), toggling any of them on/off in the dropdown also toggles those below. For example, with themes A and B listed, toggling 'B' works properly, but attempts to toggle 'A' cycle through all 4 possible on/off configurations for both A+B. Same with 3 themes (only even worse).

This is under Windows 7 / SP1 / x64 and Firefox 58.0.2 x64.