Actually, given the current demographics of SXSW, that probably IS good marketing to potential customers. SXSW now costs quite a bit and is often a hipster corporate management perk. That sounds like a good demographic for Mozilla to market to.
Lone gone are the days where SXSW was a bunch of grubby hippies listening to a bunch of crappy bands. Now it's a bunch of hipster drones listening to a bunch of crappy mainstream pop artists.
But let me second-guess the marketing team: wouldn't all that money be better spent marketing to potential customers rather than things like SXSW?