Hmm, seems to be a problem with the mobile version of the site. Maybe it is redirecting around the page? It's annoying to have to switch to the desktop version of the site (option on the 3-bar menu) to use this feature, but that would be the fallback for now.

Any updates on this?

A bug was filed in the tracking system for this last November, and the suggestion has been submitted to show the desktop page for this rather than redirecting to a non-working mobile page. I have no idea how long it will take. https://support.mozilla.org/forums/contributors/710227