Bigger Toolbar Buttons won't be updated any further. It's currently compatible up to 21.0a1 and will more than likely continue to work after that.
The only current issue is that the chat button is not resized (I believe that it's hard-coded).
I'll be working on something for Thunderbird similar to Big Buttons
Thanks for using it.
Ken SaundersAccess Firefox Project
This very simple add-on is intended for those that find Thunderbird's toolbar buttons to be too small.
It forces all toolbar buttons (excluding status bar icons) to be displayed at 38x38 pixels instead of the tiny default ones.
The 38x38 pixels size was chosen because the toolbar button's appearance degrades at anything larger.
Choosing Customize (Toolbar) > Use Small Icons will set the icons back to Thunderbird's default size.Quicker Thunderbird Add-on Installation Tip
Open the Add-ons Manager in Thunderbird.
Click on and hold the "Download Now" button on this page and drag it to the instance of Thunderbird on the taskbar > wait for Thunderbird to appear > drop onto the Add-ons Manager > Install Now.
Works on Windows, but I've been told that it works for other OS's as well.