[icebraining]

For some reason, your Firefox profile doesn't have a preferred language, but Qwant expects one. If you add one in the Preferences (option "Choose your preferred language for displaying pages"), it should work.

[cpeterso]

Seems like Firefox should fall back to the OS language of a preferred language had not been set in the browser. I wonder how that happened.

[cpeterso]

This is a Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1415146