It was discovered that the upstream security fixes in USN-764-1 introduced a regression which could cause the browser to crash. If a user were tricked into viewing a malicious website, a remote attacker could cause a denial of service or possibly execute arbitrary code with the privileges of the user invoking the program.
The problem can be corrected by updating your system to the following package versions:
28 April 2009
A security issue affects these releases of Ubuntu and its derivatives:
It was discovered that the upstream security fixes in USN-764-1 introduced a regression which could cause the browser to crash. If a user were tricked into viewing a malicious website, a remote attacker could cause a denial of service or possibly execute arbitrary code with the privileges of the user invoking the program.
The problem can be corrected by updating your system to the following package versions:
To update your system, please follow these instructions: https://wiki.ubuntu.com/Security/Upgrades.
After a standard system upgrade you need to restart Firefox and any applications that use xulrunner, such as Epiphany, to effect the necessary changes.