Very simple application to reproduce this using Telerik's AjaxManager and ASP.NET 2.0.
The button on the default page is configured to update the text box. The server side click handler updates the text in the text box but also redirects to another page. In IE9 this works fine, it redirects, but in FF5 it does not redirect.
Default.aspx...
Default.aspx.cs...
NewPage.aspx...
NewPage.aspx.cs...