I usually keep no more than two nightlies at a time.But there is only one item for each one in the Add/Remove.One is on the C drive,and the other one on the D drive.When,I tried Add/Remove,I wiped out the one that I wanted to keep,the one on the D drive.Then,I reinstalled it,and I tried the Uninstall.exe on the C drive Mozilla,and,it left it untouched,but wiped out the D drives' one again.I am hesitant in removing the mzver and mozver.dat file,since I have also NS6.1.I can see only one set of those files.I will try now the zip file install,and see if it works better.
