KM 1.0rc2 had begun to slow down and I was drawn to the Avast virus scanner. after looking at wat was being scanned, I found that the profile directory includes files

prefs-1.js through prefs-3319.js

and the last few of them are accessed every time KM does anything. This many files in the directory will slow anything down.
Can it be prevented?

I just closed KM, deleted 3,352 files and restarted KM (and it leaped up on the screen). I went staight to this forum topic, and by the time I got here there were 33 new files. This is nuts.

Right click the prefs##.js files (look for one with no number first) and check the properties, make sure it isn't read-only. There is only supposed to be "prefs.js", no number in the name, and no more than a single copy. I once had Orca (another gecko based browser) spawn a bunch of numbered copies of the prefs file when I tried to set it to read only because it kept changing the proxy option.

Also, try opening those files in notepad. If they are truly prefs files, they should be simple text files full of lines like:
user_pref("accessibility.typeaheadfind", false);

You were right. I was trying to get the favorites plugin to work and renamed a copy of the file "prefs.js.Moztmp" and set it read only. this is because KM edits this file and deletes this line:
"user_pref("kmeleon.plugins.favorites.maxMenuLength", 35);".

Apparently KM also ignores anything beyond a second dot when opening a file. After clearing this, KM promptly deleted the above line, and extra carriage returns for ease of location, from the file. I did not even have to restart KM.

prefs.js should not normally be edited, because the browser can overwrite it at will. If you want to add your own prefs, add it to a file called user.js (which the browser will only read). Or, you can add it from about:config.