So, you run three different Gmail accounts in chrome, and two different office 365 logins in Firefox. Not only can the firefox process, under you user ID, read/write chrome's cache, local data etc and vice versa, but so can your calculator app, your cpu temperature widget and your solitaire game.
Lxc can improve a bit on this, as can "containers" (lxc or otherwise restricted processes).
Lxc can improve a bit on this, as can "containers" (lxc or otherwise restricted processes).