Risk: High
The vulnerabilities in Firefox 1.5 range from high to low level criticality. Two high risk issues are addressed that cause memory corruption and facilitate XML injection, both of which arise if JavaScript is enabled. One low risk issue is that websites with long titles can cause Firefox to crash, which will repeatedly occur until the item expires from browsing history or until history.dat is deleted from the user profile directory.
It is crucial that Firefox users update to version 1.5.0.1 as a matter of urgency, as two pieces of exploit code that take advantage of some of these vulnerabilities, have been recently posted online.