Does not work, period. I use Thunderbird, another Mozilla property (still, at least in name if an unwanted bastard child) to manage RSS feeds, and there is one site with a feed that insists on delivering HTTP links in the feed rather than HTTPS. When I click on those HTTP links in the header of the feeds in Thunderbird, Firefox now refuses to open them, so I needed something to correct the site's carelessness. Smart HTTPS claims to do that but it doesn't: the links when injected into Firefox still aren't converted and still fail.