Rated 4 out of 5 stars
I used to use PageStyle2Tab before. I tried your addon now, but it creates an annoying space between tabs (about 2px).
Also, I think that it would be nice if we had the option to use css color codes of the page in order to calculate the tab color besides the screenshot method. We could even use an average of the calculated values of both methods.
Finally, you need to provide a way to make the tab text color have a value that doesn't make it "disappear" in case it is the same color as the one calculated for the tab background. This needs to work in conjunction with TabMixPlus's current/unread/other tab styles or perhaps override its settings.