How to make current icecat less crashy

[Christopher Allan Webber]

Seems a lot of us have been experiencing crashes in the current Icecat.
in Guix master.  Ricardo Wurmus gave me a nice tip that seems to have
fixed the problem here:

  <rekado> go to about:config
  <rekado> find the keys gfx.canvas.azure.backends and
           gfx.content.azure.backends
  <rekado> for both change “cairo” to “skia”
  <rekado> note that for me this results in less readable fonts

Seems to work here!  (I haven't noticed the font issue but I could just
be missing it.)