I was a satisfied Ignore Aero user, but that Add On became inoperable when my work email policy forced an upgrade to TB45. With the Extensions I am using on TB45 on Win7, I do not have the problems other commenters reported with Classic TB2, except for loss of the little X to close a tab, but the tab does close if you click where the X would be or upon Control-w as usual.
Classic TB2 has all the details right: right-sized and colored icons for Read/UnRead, Forwarded/Replied, Junk column, Signed and Encrypted email, the tool buttons are clear, good contrast of text on backgrounds throughout, venetian blind effect in the message view, and the vertical spacing allows more folders to be listed at a time than other skins (very efficient use of space) - Fantastic! There are no icons that are overly large, bright, or distracting from the main purpose of using the tool, which is a common problem with the other skin Add Ons currently compatible with TB45. I use small Icons Beside Text, and these Extensions: CompactHeader, Rise of the Tools, Allow HTML Temp, and Theme Font & Size Changer. This set up supports heavy professional use of TB45, which I would not say about TB45's default appearance. [It boggles my mind that with current display technology someone at Mozilla thinks the monochrome look of TB45 Default is a good idea for a serious email tool user.]
This must be well written SW as it has not had a version release since 2013 yet still works with TB45, but I do wonder about future updates. I am very happy with Classic TB2 and would gladly donate to its future upkeep if the developer were to add a donation button here.
This review is for a previous version of the add-on (1.3.0).