Thanks for your attempts. The real problem had nothing to do with PATH.
I tried to execute "acroread" from a shell and it all became clear.
Fedora 10 was VERY remiss in installing 32 bit libraries of many things.
To get many products to work, I had to hand install (or yum install) many 32 bit libraries.
In this case libxml was missing and so was libcanberra
Once I could run acroread in a shell, it works in firefox.