you choose what sites you want to run in the sandbox, the sandbox level and which browser to use. you can have it ask every time for the sandbox level and which browser to use for each site or you can have it remember the level and or browser.
so i could one site set to ask every time for both level and browser
one site remember level but ask for browser and vice versa
and one site with both level and browser remembered.
before running the browser in the sandbox make the browser check for updates of browser, extensions and plugins. this part probably would’t be possible but i think the rest might be doable