Remove svg blob spefic management for firefox
Sao contains a specify work arround for https://bugzilla.mozilla.org/show_bug.cgi?id=841920, but this issue is resolved since firefox50 [1], so I think we can remove the hack.
On most recent versions this code also raised an error on the browser console when trying to generate the canvas blob.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1280584