URLKey* key = (URLKey*)aKey; return mURL->Equals(key->mURL);
SupportsKey* key = (SupportsKey*)aKey; return PRBool(mSupports == key->mSupports);
  virtual PRBool Equals(const nsHashKey* aKey) const  {    URLKey* key = (URLKey*)aKey;    return mURL->Equals(key->mURL);  }