Is Browser Security getting better? That is tough to say but Firefox is definitely not leading the way. Despite all the hype, despite all the Myths, Firefox 1.x has a worse security record so far in 2006 than Internet Explorer 6.x.
The popular security site Secunia reports advisories that can include multiple security vulnerabilities of a product. The most severe Firefox Secunia advisories tend to get posted at each version update of the browser. These version update advisories mislead someone looking simply at the advisory totals:
Firefox v1.5.09 - 12/19/06 - SA23282 - 12/19/06 - 10 Vulnerabilities
Firefox v1.5.08 - 11/07/06 - SA22722 - 11/08/06 - 5 Vulnerabilities
Firefox v1.5.07 - 09/14/06 - SA21906 - 09/15/06 - 8 Vulnerabilities
Firefox v1.5.05 - 07/27/06 - SA19873 - 07/27/06 - 13 Vulnerabilities
Firefox v1.5.04 - 06/01/06 - SA20376 - 06/02/06 - 10 Vulnerabilities
Firefox v1.5.02 - 04/12/06 - SA19631 - 04/13/06 - 27 Vulnerabilities
Firefox v1.5.01 - 2/01/06 - SA18700 - 2/02/06 - 8 Vulnerabilities
Simply looking at the advisories between Firefox 1.x in 2006 and Internet Explorer 6.x in 2006 gives a misleading 10 to 14 advisory "win" for Firefox but once you add up the actual vulnerabilities for each it is clear Internet Explorer 6.x has been the more secure browser so far in 2006:
Firefox 1.x - 13 Advisories = 88 Vulnerabilities
Internet Explorer 6.x - 14 Advisories = 36 Vulnerabilities
Internet Explorer 6.x more secure than Firefox in 2006.