Why do we provide user with a choice of ok/cancel here?
I expect that this script would be run by non-techy people and they could be easily scared with scary message and illusion of choice.

If this is intended to be a fatal error, then could you please provide more context of what we were looking for and user can do to fix it, use error icon and only one button that cancels program execution.
If this is not a fatal error, then user does not need to know that we'd some problems if he can not help us to fix it.

Or you could call it from around -- Load page from browser, to search for browsers in cycle and provide user with some information on what this script does and what are we looking for.
Or even make GetPageContents() parameterless to choose the right browser inside.