Rated 5 out of 5 stars

Finally a return to the way Seamonkey looked before the modern minimalist look (which is ergonomically inferior) took over the world with Windows 10. Thank you.

One suggestions. On some displays the grey is a tad dark. Would it be possible to make grey variable?

This review is for a previous version of the add-on (0.4). 

I'm just glad there are people out that that feel the same about new design ideals as I do.

Anyway, I don't think making the grey variable is really possible (if it is, it is way beyond my scope), sorry!
But feel free to unpack the xpi file and adjust it yourself (fair warning: it may take a while to do that).