The procedure entry point ??1nsSupportsWeakReference@@IAE@XZ could not be located in the dynamic link library xpcom.dll

When I start firefox after doing the above steps. Seems to be generated as a result of that spellcheck.xpi installation. If I go in and prune the stuff it installed in the components folder, then the error message goes away.

Oh, also, spell checking still doesn't work, presumably because the spellcheck DLL can't start because of the above error.