Update pixel-art class to work with Firefox.
Update pixel-art class to work with Firefox.

Firefox stable does not yet support image-rendering:pixelated.
https://bugzilla.mozilla.org/show_bug.cgi?id=856337

The latest version of Safari no longer requires the -webkit prefix, so
remove that, too.

tswast/who-goes-first,whogoesfirst/who-goes-first,whogoes1st/whogoes1st,whogoes1st/whogoes1st,bananajuicellc/who-goes-first,bananajuicellc/who-goes-first,tswast/who-goes-first,whogoesfirst/who-goes-first,whogoesfirst/who-goes-first,bananajuicellc/who-goes-first,tswast/who-goes-first,whogoes1st/whogoes1st