Normally, there is no need to actually "exit" out of the browser. Once you switch focus to another application (and the browser is no longer visible), it will remain in memory until the operating system needs more memory. When this occurs, Android will take a "snapshot" of the current state (ie. which URL you are browsing) and then reclaim the memory that the browser was occupying. In most circumstances, you won't notice any hit on performance while keeping the browser in memory until it's needed.
To answer your question though, no. As far as I know, the only way to exit out of the browser is to either hit the back button until all windows are closed, manually close the application from within settings or a task manager, or to let Android close it on it's own when it needs the memory. The only times I would need to manually close the browser would be if say a web page that accesses your location somehow causes the GPS to hang (has happened to me on google's homepage before), or if I was getting ready to use any memory intensive application where pauses to close a program could rewsult in a glitch, such as when recording video or audio.