It seems there is some sort of issue in Firefox when clicking a <a> that has been set to a button with text set to 'disable' and only an icon is visible.

you can see it happening here:

http://wiki.jqueryui.com/Buttons

simply click or right click one of the <a> buttons (not the <button> ones) where only an icon is showing (and no text), you can see them under   ' 4 - Markup & Style:' in the anchor section. the browser seems to pause while it 'selects a large area around the anchor.

this doesn't happen in Chrome/Safari/IE.