Users should avoid links in unsolicited email messages and untrusted URLs regardless of which browser they use.  Based on past experience, the Mozilla foundation has a priority on security, so I'm certain this will be addressed soon with a new release of Firefox.

Firefox/Deerpark all versions - Critical Security Warning
http://news.zdnet.com/2100-3513_22-5856201.html
http://techrepublic.com.com/2100-1009_11-5856201.html
http://secunia.com/advisories/16764/
http://security-protocols.com/advisory/sp-x17-advisory.txt

Tom Ferris has discovered a vulnerability in Firefox, which can be exploited by malicious people to cause a DoS (Denial of Service) or potentially to compromise a user's system. The vulnerability is caused due to an error in the handling of an URL that contains the 0xAD character in its domain name. This can be exploited to cause a heap-based buffer overflow.

Successful exploitation crashes Firefox and may potentially allow code execution but requires that the user is tricked into visiting a malicious web site or open a specially crafted HTML file.  The vulnerability has been confirmed in version 1.0.6, and is reported to affect versions prior to 1.0.6, and version 1.5 Beta 1.