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Open EDGE settings by typing edge://settings/ in the address bar or by clicking on the three dots from the top right corner > Settings.
From the left sidebar, click on System and Performance. If you’re looking to protect only certain sites from being made inactive, сlick the Add button that is next to Never put these sites to sleep
Type in the websites you want to always keep active, and enter only the main domain of a website
Firefox doesn’t have this functionality
Safari doesn’t have this functionality