It won't be the last, but it will certainly be "famous" because it is the first one found after Firefox 3.0 was launched - here's the first security flaw found just 5h after the release of the latest edition of Mozilla's famous browser (and Guiness Record holder, with ober 8 million downloads in the first 24 hours.)
Which leads me to:
Finding these flaws can become a very lucrative endeavour!
Whoever finds such a security risk, can head to Zero Day Initiative and be rewarded for it.
They'll keep the details secret until the issue is fixed, and release it later on, so everyone else can learn from these mistakes.
The amount varies according to the gravity of the flaw, but can reach tens of thousands of dollars, and even include a paid trip to Las Vegas to attend DEFCON, BlackHat Conferences, and BlackHat Training.