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).

Rated 3 out of 5 stars

In mozapps > plugins > pluginProblem.css, you mixed up the blocked icon and the click-to-play icon and used the wrong images.
The blocked should be:
:-moz-handler-blocked .icon,
:-moz-handler-vulnerable-updatable .icon,
:-moz-handler-vulnerable-no-update .icon {
background-image: url("chrome://mozapps/skin/plugins/contentPluginBlocked.png");
-moz-user-focus: normal;
}

This review is for a previous version of the add-on (0.1). 

I mostly just copied that over.
Thanks for the information, though - I'm going to fix it, along with the picture to the left of the tabs, which has the old blue tint (notice that?).
Expect a new version..next week I suppose.

Rated 5 out of 5 stars

I've always loved the SeaMonkey Gray Modern theme, had one similar when there was the Mozilla browser. Thanks for making an updated one for the newest SeaMonkey!

This review is for a previous version of the add-on (0.1).