fixes a rare case of the popup being invoked right after switching to a lazily restored tab-on-demand, which doesn't have an URL yet in FF or has an URL but not the content script in some Chrome forks that implement tab-on-demand
kinda fixes#155
as per spec the fragment portion is ignored in @-moz-document:
https://www.w3.org/TR/2012/WD-css3-conditional-20120911/#url-of-doc
but we still respect url("foo#hash") set in userstyles
because the spec is outdated and doesn't account for SPA sites
collateral damage: simplified URLS.supported()
