Works well with Firefox Nightly v60.0a1 on Android v6.0.1. Would be vastly improved if regular expressions (extended form) could be used to match against entire URLs. Currently, only the absolute string of the top-level hostname can be checked. But with regular expressions, it would, for example, be possible to match "^[fhttps]*\:\/\/www\.google\.co(m|\.[^\/]*)\/imgres\?" against URLs, in order to specify the user agent for displaying an image returned from a Google image search. Although this is a seemingly-specific example, with extended regular expression matching, anything would be possible, as they provide maximum URL-matching flexibility.