Edit: this trick stopped working as of Firefox 31 (in Nightly build as of May 2014). Join the comments section to help finding an alternative.
- Set
-moz-appearance
tonone
. This will "reset" the styling of the element; - Set
text-indent
to0.01px
. This will "push" the text a tiny bit[1] to the right; - Set
text-overflow
to''
(an empty string). This will change anything that extends beyond the element's width to... nothing - and this includes the infamous arrow!