I get that file not found as well. And yes, Firefox is my default browser and has been so fo r a long time. I just uncheck the View Readme while installing. If I REALLY want to see the readme at a later date, it works fine doubleclicking it from whereever it installed to. Firefox can open THAT, but I think the Readme launcher assumes you've got Internet Exploiter as your default browser...

FREEBIES! | My Gallery | My Store | My FB | Tumblr |
You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.