Rated 4 out of 5 stars
At first, version 0.2.1 seemed to fix the width issue in "Options" on Thunderbird.
However, after checking other windows to see everything was correct (everything was, besides "Return Receipt Settings", under "Email Accounts Settings", where the scroll boxes were -- very slightly -- cropped on the right), the old/cropped width of the "Options" window returned inexplicably.
I believe it happened after I toyed with the add-on's options (BTW, enabling "Icons" makes scroll boxes appear on the options window of the add-on; it should be made slighty larger to prevent this), but I can't be 100% sure it is what caused the bug to return.
I've also tested this 0.2.1 version on Firefox 3.6 : some windows suffer from this bug.
Last but not least, I have one suggestion to make : an option to have the icons be brighter, brighter-reverse, grey, regular (faded -- like it is by default), or normal (always regular, no matter if they're hovered or not), without having to overwrite mosaic.png would be pretty sweet.
4 stars, because each version it gets better.
i enlarged the width of the options dialog, that should fix it
as for adding the mosaic.png files, wait for 0.2.2