Yesterday Google promoted Chrome 25 from beta to production status and fixed nine high severity vulnerabilities. Google also disabled the MathML extension indicating that it is not ready for production use yet.
Earlier this week, Mozilla came out with Firefox 19, that now includes its own PDF reader making the installation of the often attacked Adobe Reader unnecessary and fixing a number of vulnerabilities in the release.
Two weeks ago, Microsoft published a new version of Internet Explorer that addressed a record number of 12 critical vulnerabilities.
I believe all of them are shoring up defenses for the upcoming CanSecWest conference on March 6-8 in Vancouver, where the ZDI Initiative will hold its annual PWN2OWN competition, in which some of the world’s leading vulnerability and exploitation specialists compete for the fastest and most elegant way to break through browser defenses and take away the top prize of up to US$ 100,000 for browsers and US$ 75,000 for plug-ins, which are under fire for the first time in this competition.