Thinking about this a bit more: the most likely use for this specific license grant I can come up with is a 3rd party partnership similar to pre-acquisition Pocket.
Imagine if on first startup Firefox offers you to show website recommendations. Maybe a prechecked checkbox. If you don't say no, they send anything you type in the address bar to some third party, that third party throws that in a recommendation system and spits out websites you may want to visit, which Firefox then shows in the new-tab page. This license grant would cover that. They would be using a license on content I input (all my keystrokes in the address bar) to help me experience online content (recommendations for new content) as I indicate (they asked). In principle recommending me websites based on all images I upload with Firefox would also be covered, though that's a bit far fetched.
Of course in the EU you'd probably have pretty strict consent requirements because of the GDPR, same with other jurisdictions with strong privacy protections. But in places with weak privacy protections the grant in question should cover all bases to pull something like this
Imagine if on first startup Firefox offers you to show website recommendations. Maybe a prechecked checkbox. If you don't say no, they send anything you type in the address bar to some third party, that third party throws that in a recommendation system and spits out websites you may want to visit, which Firefox then shows in the new-tab page. This license grant would cover that. They would be using a license on content I input (all my keystrokes in the address bar) to help me experience online content (recommendations for new content) as I indicate (they asked). In principle recommending me websites based on all images I upload with Firefox would also be covered, though that's a bit far fetched.
Of course in the EU you'd probably have pretty strict consent requirements because of the GDPR, same with other jurisdictions with strong privacy protections. But in places with weak privacy protections the grant in question should cover all bases to pull something like this