Condition:
Browse to an FBA (Forms Based Authentication) SharePoint 3.0 site using the url like http://mydomain/ and instead of seeing the login page you get a 403 Forbidden. Try it in Firefox and works. But then you try it in http://mydomain.com/default.aspx and you are correctly redirected to the login page.
Strange, no? Let me guess, you also have Office Live Components installed on the client attempting to access the site?
If so, the Windows SharePoint Services Cumulative Update Hotfix Package will fix the problem.
