Rated 5 out of 5 stars

I've been using Montezooma, which is fine, except that it appears only on the Status Bar, where it is inconvenient and miniscule.

I've tried everything I can think of to display my messages in a consistent and readable size. Until TB can do that, your Add-On is my lifesaver.

This review is for a previous version of the add-on (0.0.6). 

Thank you for the kind words, review, and rating.

If you use the Stylish add-on, you could add the following CSS as a userstyle. I use it myself along with Theme Font & Size Changer.

html * {
font-size: 24px !important
}

You can of course change the font-size value.

You could also add that code to a userChrome.css file.
http://kb.mozillazine.org/UserChrome.css

https://addons.mozilla.org/en-US/thunderbird/addon/theme-font-size-changer/ (works with Firefox too)