2013
FlowType.JS — Responsive web typography at its finest: font-size and line-height based on element width.
by 3 others2010
The Firefox Input Button Line-Height Bug
Basically, Firefox is setting the line-height to “normal” on buttons and is enforcing this decision with an !important declaration. This is a frustrating decision on their part, particularly considering (as Eric Meyer has pointed out at great and detailed length), line-height: normal is anything but.