Toolbar Navigation - Previous/Next button enhanced script

I've found a few topics on how to add the standard skin back/next script to a skin, for that I thank everyone.  I would like to take it to the next level and make it behave even more like browser buttons meaning when a user has never navigated to a 2nd topic the Back button is unavailable (gray), when they have navigated to multiple topics the button is available (blue). Same for the next button.

Standard script:

For back:

javascript:history.go(-1);

For next:

javascript:history.go(1);

Any ideas?

I believe I saw it somewhere before and now I can't find it.