Our latest internal build released this week includes support for Firefox 4. The next official release will be out late this month or early May.
If you'd rather not wait and stay on your current version of WebAii Framework, a quick Google search will point you to older versions of FF. Look for version 3.x.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items