There are a couple of features that should be disabled when running Firefox under App-V 5: Users can even set a virtualized Firefox as their default browser. With App-V 5 there’s no such change to the way users might interact with Firefox. Typically, virtualizing an application changes the user experience due to the introduction of isolation. It’s important that Firefox is configured correctly for virtualization by disabling specific features. Before embarking on sequencing Firefox, please refer to this companion article - Prepare Mozilla Firefox for Enterprise Deployment and Virtualization - which covers configuring a Firefox installation for virtualizing. It’s a simple task to virtualize Firefox, as it lends itself well to application virtualization however getting it right takes a little preparation.