Mozilla today fixed a vulnerable in how Apple QuickTime Media-Link files contain a qtnext attribute that could be used on Windows systems to launch the default browser with arbitrary command-line options. Although the problem appeared to be resolved earlier this year, researcher Petko D. Petkov and others found recently that it could still be exploited.
A previous fix in July's Firefox version 2.0.05 was intended to resolve this issue, but, according to Mozilla, "QuickTime calls the browser in an unexpected way that bypasses that fix." Also, Apple's own fix in the release of QuickTime 7.1.5 last March failed to resolve the issue.
Finally, Mozilla notes that the upcoming release of Firefox 3 (Gran Paradiso) Alpha 8, expected today or tomorrow, does not contain the fix for this vulnerability.