On Windows, Ctrl+W will close the current tab in a flash, no matter which browser you're using (Chrome, Firefox, or Edge), but you will lose whatever was in the window at the time. Another option would be to minimize all the currently-open windows with Win+D. This leaves a blank desktop, which might be non-incriminating, but does make it look like you're not doing any work. We recommend a quick Alt+Tab combination, which will switch you into a different app (usually the one you were using before you opened the browser). Just make sure the app you're switching to is a work-appropriate one.