Bug 964529 pre-patch:  Make things that were syntax errors prior to enabling scientific notation continue to be syntax errors, by changing e+ to x+.
Bug 964529:  Support scientific (exponential) notation for CSS <number> values, including percentages and dimensions (but not <integer> values).  r=SimonSapin

Resolved for <number> on 2012-08-15:
http://lists.w3.org/Archives/Public/www-style/2012Aug/0900.html

Resolved for percentages and dimensions in CSS teleconference 2013-04-17:
http://lists.w3.org/Archives/Public/www-style/2013Apr/0428.html