This is just a minor optimization to ensure we don't reparse the user stylesheet just because the CSSStyleSelector went away (which can happen if you add/remove sheets or for some other reasons).
Created attachment 39092 [details] Patch
Comment on attachment 39092 [details] Patch OK. r+, cq-. Hyatt can set cq+ himself if he wants the bot to land this for him.
Fixed in r48181.
this fix broke simple selectors in my user stylesheet. #someId and div#someId are no longer recognized; i have to use div[id="someId"]. i'm using tiger on PPC if it matters.