Well, that was easy. When I opened the terminal,before I even typed anything, there was a message abut being unable to chmod my temp folder. I actually missed it at first & typed "firefox" & got "unable to write to /home/davepet/tmp" Same message on typing "thunderbird".
I checked /home/davepet/tmp & sure enough root owns it now. Changed ownership back to davepet & they are all working now.
Thanks for the tip,