Firefox just updated and all my settings, passwords and add-ons were wiped out. Why?

I have it installed on D drive. Could that have been the problem? Does this program not even know where its installed so it can updated itself without causing so much havoc? How could any thinking person ever design something to do this without warning us first? This causes millions of hours of wasted time redoing everything by their users. Its just so thoughtless and inconsiderate.

Your old profile probably still exists, you just need to find it. Did you install an older version of Firefox? By default older versions make a new profile as sometimes downgrading a version can cause a problem with profiles.