A coworker just pulled me over to help with a javascript issue, and I noticed on his screen that some of our input elements looked totally whacked out in Firefox. Not so in -webkit. I dug around a bit and found this handy reset:
input::-moz-focus-inner,
button::-moz-focus-inner { padding:0; border:0; }
Now the buttons are happy in both browsers! Hooray!