Zoomy is an extension that allows you to modify the toolbar buttons size.
Provides toolbar buttons to increase, decrease and reset the text size (for the current tab). They function like the equivalent items on the View menu.
(After installing use View > Toolbars > Customize... or equivalent to add the buttons to a toolbar.)
· Thunderbird 1.0 - 1.5.0.* ALL
Zoomy still works with Firefox 2.0 _if_ you fix the .xpi file. Briefly, rename the zoomy .xpi file to a .zip file, extract files. Edit the instal.rdf file and change maxVersion to 2.5 (so you don't have to fix it for 2.1, etc.), re-zip, rename to .xpi, and it will then install and work.
One method that works very nicely is to use the add-on Nightly Tester Tools, which makes the whole process of keeping these nice add-ons functional as Firefox moves up its evolutionary ladder.