If the software was blocking at a lower level on the network stack and not just in the browser, then the answer is probably multiplayer games. Presumably OP was

If the software was blocking at a lower level on the network stack and not just in the browser, then the answer is probably multiplayer games. Presumably OP wasn't doing this just last year, but in the late 90s and early 2000s when Linux gaming wasn't a real thing yet.