Since we're touching this file, it'll be good to do some changes;
I'm not in favor of wrapping prefixed rules in `if`s; moreover, in the meantime IE10, Fx and Ch adopted unprefixed version of linear-gradient and perhaps very soon the prefixed versions will be removed.

I think we should put sth like described here, without conditionals:
 https://developer.mozilla.org/en-US/docs/Web/CSS/linear-gradient#Cross-browser_gradients (keep -moz and -webkit for compat with Safari and Fx 3.6, and add standard one as last)