Sorry, no idea what that is or how it works. Not a Firefox add-on, or not listed at the official add-ons website. Although it looks like the developer submitted that to application to AMO - but apparently it wasn't accepted at AMO for hosting. Try the developers own web site for help with that application. https://mediahint.com/support https://mediahint.com/support/help-center

Media Hint has been one of my Firefox Add-Ons for approximately two years.

Regardless - it's a 3rd party application / add-on that isn't currently available from Mozilla. It's up to the developer of each add-on to support what they made; I try to provide support for add-ons where I can - but not for add-ons that aren't available from the official Mozilla add-ons website. I have even installed an add-on to check it out (on rare occasions), but only for add-ons that have been "cleared" / approved by Mozilla.

Maybe someone else will see this thread later today who is familiar with Media Hint and can help you.