[Toaster] Reference browser for testing purposes

[Barros Pena, Belen]

We should probably have raised this question earlier and had a plan in
place, but hey, better late ... The question is: which browsers should we
be using as a reference for QA purposes? Our guideline here is decent
HTML5 compatibility, but we never qualified what 'decent' means.

The other reference we could use is traffic to the Yocto Project website.
Visits are mainly coming from Chrome 32 and 33 on Windows, and Firefox 26
and 27 on Linux. I can put together more detailed numbers if anybody wants
to see them. 

Those might be a bit too cutting edge, but could guide our decision
somehow. QA is currently testing with Firefox 11: that is probably too
old. 

In light of the above, any suggestions about which browsers we should use
for testing?

Thanks!

Belén