Workarounds would either have Extended Menu to be aware of JoomFish (which seems unnecessary since it is not supposed to call any method anymore) or remove the backward compatibility to MambleFish completely. The best solution might be to make JoomFish not pretend to be MambleFish anymore.
This was found and tested by a user and not myself:
In
mambots/system/jfdatabase.systembot.php there is the following line which you can uncomment/remove:
$GLOBALS[ 'mosConfig_mbf_content' ] = '1';
You may also find an old entry for
mosConfig_mbf_content in your
configuration.php.
Make sure it is either removed or set to
'0';
Feel free to raise a bug report at JoomFish (if there is no such entry already).