Only "recommended" addons can be added to Firefox on Android devices (?)

When using the Firefox Addons Manager on three different tablets (and a phone) in recent days, it has only been possible to add the few addons listed under “Recommended” to the browser. Whilst I’m told there should be an option to find further addons below this list, this is not shown on any of the four Android devices I have checked on. Is there supposed to be a search box there or something? If it is supposed to be there, it is not.

Navigating to in the browser does not help either. If you tap “add to Firefox” on any of the addons you find there, the browser downloads an xpi file. When you tap on the file, the device informs you that “no app on your device can open this file”. One tablet even attempts to open the file in an inappropriate app (Simon Tatham’s Puzzles!).

Any advice would be gratefully received. I would like to install a number of addons to enhance my experience on Google/YouTube, but this is not currently possible on Firefox on Android.

Installing arbitrary addons is not yet available.
General support for extensions on Android should come in December.

Thank you for the information.