Unlike Firefox 7.0, the release notes for 3.6.23 is rather simple and seems usual.
Firefox 3.6.23 fixes the following issues found in previous versions of Firefox 3.6:
Fixed several security issues.
Fixed several stability issues.
Within the security issues addressed, Mozilla labelled 3 Critical, 1 High and 1 Moderate.
Firefox 3.6.23 can be downloaded here
UserAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:126.96.36.199) Gecko/20110920 AlexaToolbar/alxf-2.14 Firefox/3.6.23