Mozilla Patches 14 Bugs in Firefox 4
Thirteen of the flaws are tagged as critical and one is labeled as low impact.
Most of vulnerabilities in Firefox 4.0.1 are memory-safety-related issues. According to the advisory:
Some of these bugs showed evidence of memory corruption under certain circumstances, and we presume that with enough effort at least some of these could be exploited to run arbitrary code.
Firefox developers are currently moving forward on Firefox 5, which is scheduled for release by the end of June.