Rated 5 out of 5 stars

but it doesn't for me: Thunderbird 13.0, Windows 7 64. Any suggestions are appreciated.

After an almost immediate, polite and informative response from the developer, I did the following: disabled Theme Font and Size Changer, installed Bigger Toolbar Buttons, works like a charm, re-installed Theme Font and Size Changer, everybody's happy now. Haven't tried it on the Linux Mint side of the computer, but I expect no problems.

Now a request: there are still a bunch of tiny icons to click on, such as the x on the tabs, which do not change size. Either its my set up, or Thunderbird's folks haven't looked at the needs of large high res displays. It could very well be that I need to change something, any thoughts appreciated.

Hi,

This add-on has been tested on Windows in Thunderbird 13 and 14.0a2 and functions properly for me.

Do you (by any chance) have "Use Small Icons" checked? in the Customize Toolbar window?
Do you use a theme for Thunderbird?
Any custom userstyles?

I'd like to help you get it working and I sincerely appreciate the 4 stars gesture. :)