Few days ago Mozilla Firefox 1.5.0.3 installer was found on their FTP but they have not announced it on their website yet.
Today, Mozilla Firefox 1.5.0.3 is oficially released and it contains only 1 but very important security fix for denial of service vulnerability.

Title: Deleted object reference when designMode=”on”
Impact: Critical
Date: May 2, 2006
Reporter: Martijn Wargers, Nick Mott, splices
Affects: Firefox 1.5
Fixed in: Firefox 1.5.0.3

Description
Martijn Wargers and Nick Mott each described crashes that were discovered to ultimately stem from the same root cause: attempting to use a deleted controller context when designMode was turned on. This generally results in crashing the browser, but in theory references to deleted objects can be abused to run malicious code.
“splices” reported the same crash at the fan site MozillaZine and on Bugtraq, incorrectly describing it as a buffer overflow.
Older clients, including Firefox 1.0.x and the Mozilla Suite 1.7.x, are not affected.

Workaround
Temporarily disable JavaScript until you can upgrade to a fixed version. (Now you have a fixed version, so you don’t need to temporarily disable JavaScript.)

[ Download Mozilla Firefox 1.5.0.3 ]

P/S: For your info, I’ve also found Mozilla Firefox 1.5.0.4 on Mozilla’s FTP 😉