Linden Lab has stated they intend to begin rolling out Server Side Appearance (formerly known as Server Side Baking) on July 9th or shortly thereafter. It is of paramount importance to your user experience that ALL our users upgrade to this 4.4.1 version before the 9th of July. Even our 4.4.0 users should upgrade because 4.4.1 contains some additional SSA code from LL.
Firestorm's support team recommends a clean install. If you don't know how to do it: first you need to backup your settings (next video can help you) and follow this instructions.