Hello,
In Task Manager, the categorization of an application as a background process or an app depends on how Windows perceives its resource usage and activity. The firefox may move to the "Background processes" group when it's not actively using CPU resources or when all of its tabs are minimized or in the background.
However, there is no direct setting that allows you to force an application like firefox to always stay in the "Apps" section of the Task Manager regardless of its activity level. The grouping behavior is automatic and managed by the operating system.
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