I may have fixed it. I noticed the file in question was 0kb in size. Since it had "cpy" in the name, I deduced that it was supposed to be a copy of the other file, SuperShieldHook32.dll... especially since SuperShieldHook64.dll and SuperShieldHookCpy64.dll were the same file size. So I simply made a copy of SuperShieldHook32 and changed the name to SuperShieldCpy32... hopefully that's what it wanted. At least it got rid of the annoying popup error.
Not sure what section this belongs in, but apparently not here. Yeah, this is actually happening for more than just Firefox. It's annoying, because I'm sort of a perfectionist.
I start firefox, get this error box, click "ok" and it works fine, and the PCMatic shield plugin attached to the Firefox browser seems to be working. But any time I close it again and reopen, I get this error box about the dll...