Comments such as yours are missing the point.

Mozilla's ToS applies for Firefox's use, and this is literally written by Mozilla themselves:

“Your use of Firefox must follow Mozilla’s Acceptable Use Policy”

There's no distinction between the browser and Mozilla's online services here.

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And even if it were referring only to features such as “profile syncing” (and it doesn't refer only to that), does this mean that people can't have bookmarks to porn? And why would Mozilla care about how people use profile syncing at all? I thought it was e2e encrypted.