Firefox Nightly crashes when trying to call getContext('2d') on a canvas that is non-visible (display:none) and is used as a background for another element (background:-moz-element(...)). Code to reproduce: https://gist.github.com/anonymous/8922683
Created attachment 8459142 [details] Test I could not reproduce on Linux with this test case. Reporter, could you check if it does for you?
Can't reproduce it anymore either in latest Nightly.