If you have the current beta, there is a section of the "Perform a Window Function" window that will display the window title and process name of the active window.
Otherwise, you can use the "{ACTIVEWINDOWTITLE}" token to try and find out the window title of your browser, while you have it selected.
You could also try using the process name, but that doesn't work with browsers that run more than one process.
However, you won't be able to send Ctrl-R (or F5, which does the same thing with a single key) to the window without losing focus even if you do target it specifically. VoiceAttack will give the target focus before sending any keypresses (as Windows expects you to send input that way).