Can't add Spot as search engine on Firefox

Hi all,

When I try adding Spot to my Firefox search engines (right click on address bar > Add Spot) I get this error message :

Firefox n’a pas pu télécharger le plugin de recherche à partir de :

Meaning: Firefox could not download the search plugin from: htlps://

I still can add it in my bookmarks and choose a search shortcut, however I can’t set it as my default search engine.

Thanks for your help!

using Mull (firefox based)
i was not abble to add it as you relate (right click on address bar),
But at my second attempt that was done from the settings, i was abble to add it