Mozilla and Google made some quick moves last night to patch up their browsers. In Chrome's camp, a batch of bugs went down, but also a high-level Mac security flaw that Google hasn't released details for.
On the Firefox side, lots of small stuff was cut down in Firefox 4 Beta 6, but a major fix should prevent Mac users from experiencing white shading over web pages that prevents typing due to a plugin handling error. In both cases, grab the update as soon as you're able. [Chrome Releases, Beta 6 release notes via CNET, CNET]