Risk: High
Mozilla has only recently released the newest version of Firefox - version 1.5.0.3, which fixed a variety of security flaws, but new flaws have since come to light that Secunia has classified as 'highly critical'.
Firefox users could experience a Denial of Service attack if an attacker makes the browser crash by maliciously coding a website, which can then permit arbitrary code execution. The flaws affect a variety of platforms, including Mac OS X. Older versions, including Firefox 1.0.x and the Mozilla Suite 1.7.x, are not affected.
The recent introduction of Firefox version 1.5.0.3 was intended to fix a significant number of flaws found in previous versions, so it will certainly be interesting to see the volume of subsequent vulnerabilities found in Firefox.
Those who use Firefox should receive an automatic update notification. If not, select 'help' from the dropdown menu and select 'check for updates'.