Right now it's returning a plain JS empty array. It should be returning a Uint32Array according to the spec: http://www.khronos.org/registry/webgl/specs/latest/#5.14.3
I believe the patch in bug 745897 fixed this.
I updated the gl-get-calls test to check for types of arraybuffers
I tested that in today's Nightly, and this is indeed fixed. Thanks for pointing out where that test lived
Yep, removing webgl-test-needed. Thanks!