If you haven't already done it, go get the new version of Firefox (v2.0.0.13). It fixes ten security issues of varying severity, many of which are critical.

An accompanying update of Mozilla's Thunderbird Email client won't be out for several weeks. David Ascher who is the head of Mozilla Messaging addressed this on his blog :

"there’s a Firefox 2.0.0.13 release coming up, which fixes some security bugs. Some of those are in the part of the code that is shared with Thunderbird. There will therefore be a matching Thunderbird 2.0.0.13. The only question is when. At the scheduling meeting, it was clear that the ideal scenario (near-simultaneous security releases for Firefox and Thunderbird) was simply impossible, mostly because of resource contention. Some of those resource contentions are due to not enough automation for the Thunderbird release process, and some of it is the consequence of not enough people with the right training — one of the factors that led to the creation of Mozilla Messaging. After careful weighing of the various options, we all agreed that Thunderbird 2.0.0.13 will have to release several weeks after Firefox 2.0.0.13."