I've been using Fabien Doiron's Box-Shadow Method to create multi line padded text for a while. Just recently I had to find out that this isn't working anymore in later versions of Firefox.
Turns out starting with Firefox 32 Mozilla has introduced
text-decoration-break: split as default. Setting it to
box-decoration-break: clone; does the trick.
Thanks to Chris Coyier for pointing this out.