Mozilla Firefox and Opera this week issued patches for a number of vulnerabilities in their browsers.

Firefox contains fixes for 13 vulnerabilities, four of which which could be remotely exploited to install malicious software on a user's machine.

Mozilla, fresh off the widely publicized release of Firefox 3, also announced it would end support for its sophomore browser version in December.

The company said on Wednesday that Firefox 3, released June 17, was downloaded more than eight million times in its first 24 hours -- setting an apparent Guinness World Record. The new browser touts enhanced malware and phishing protection.

Meanwhile, Opera version 9.51 was released to plug a number of security holes, according to the SANS Internet Storm Center. One of the patches fixes a bug that could have allowed arbitrary code execution.