Within the first 5 hours of the release of Firefox 3, Tipping Point, a research organization for vulnerability analysis and discovery advised they had found a vulnerability. Now before you go adding this to your list of reasons not to download and install Firefox 3, this vulnerability also affects Firefox 2. For security reasons, not much information is being released about this vulnerability other than:
Successful exploitation of the vulnerability could allow an attacker to execute arbitrary code. Not unlike most browser based vulnerabilities that we see these days, user interaction is required such as clicking on a link in email or visiting a malicious web page.
The good news is there is no known public exploit for this bug at this time. No word at this time if this is going to cause Mozilla to do a Firedrill release of Firefox 3.0.1 sooner than the planned release in about 4 to 6 weeks.
News Sources:
The Firefox Extension Guru's Blog 
[…] to slow check-in on patches which had delayed the initial code freeze. However, because of the Firefox 3 Vulnerability from earlier this week (that also affects Firefox 2), the release schedule for Firefox 2.0.0.15 now […]