"I'm now in the terrible position of choosing to deploy a Firefox 4 release with potentially unpatched vulnerabilities, reset the test cycle for thousands of internal apps to validate Firefox 5 or stay on a patched Firefox 3.6.x," Walicki said in a comment appended to a .

When Mozilla retires Firefox 3.6, that last option won't be available to Walicki and IBM.

to tout its support policies for Internet Explorer (IE).

Yesterday, Ari Bixhorn, director of IE, published an open letter to Walicki urging him to consider switching from Firefox to IE8 or IE9. "I think I speak for everyone on the IE team when I say we'd like the opportunity to win back your business," said Bixhorn.

The retirement of Firefox 3.5 will affect only a small fraction of Mozilla's active users. According to Web metrics company Net Applications, Firefox 3.5 accounted for just 6% of all copies of Mozilla's browser used in May.