FR is one of the most common abbreviations in comment sections. On its own it works as agreement โ someone posts a relatable take and the replies fill up with "fr." Attached to your own statement, it signals sincerity: "this is the best burger in the city fr."
The doubled form "fr fr" started as ironic exaggeration but is now standard. You will also see it combined with other slang, like "fr no cap" or "ong fr," stacking multiple sincerity markers for comedic effect. It is casual, lowercase-by-default, and reads as out of place in formal brand copy unless the brand has an established playful voice.
