There is no warranty whatsoever, it's more a joke to ensure that users are aware of what they are about to do). Use the checkbox there to avoid the warning in the future.Read answer to: "HowTo: Firefox Disable Default PDF Viewer / Plugin"
Firefox: about:config – “I’ll be careful, I promise! warning button
by Nix Craft on March 7, 2013· LAST UPDATED March 7, 2013