Work around a crash bug in Firefox 27.
Work around a crash bug in Firefox 27.

Fixes #1869

Martii/greasemonkey,Ventero/greasemonkey,the8472/greasemonkey,Martii/greasemonkey,HasClass0/greasemonkey,HasClass0/greasemonkey,Ventero/greasemonkey,the8472/greasemonkey