Firefox > Options > Toolbar Layout > [ ] Use Small icons

You can also look at this extension:

• Theme Font & Size Changer: https://addons.mozilla.org/firefox/addon/162063/

Firefox > Options > Toolbar Layout > [ ] Use Small icons Does not work in firefox 4.0. The icons are small by default. Use small icons feature only makes them smaller.

I'm trying ver 4.0, i want to make the icons As big as they were in ver 3.6.

@cor-el: This extension is handy because you can change the size of the text, but it doesn't solve the problem of the small buttons (since it doesn't changes anything about that)

You can increase the String pref layout.css.devPixelsPerPx from 1.0 to 2.0 in 0.1 steps to see what works best.
In current Firefox versions this pref is a String value parsed to a float and allows to fine tune the dimensions of all elements (user interface and web pages) more precisely.

• http://kb.mozillazine.org/about%3Aconfig

Little addition to cor-el's solution (thank you!): the steps don't have to be 0.1, smaller (0,15, 0,205 etc.) are also possible and should let everyone adjust it just the way one prefers it.

Thanks cor-el. That was a god send. If anyone out there knows how to create an Add-On that would do that automatically for all the visually impaired people that would be great! A simple Add-On that would do the exact same thing with the options button giving you a choice, 1.0, 1.15, 1.30, 1.5,, 2.0, or something like that would be great for the millions of low sighted people who may not be computer hacking geeks. That would be a nice gesture from someone at Mozilla. Thanks JWINSA

I agree, something that is quick and easy would be nice.