Currently the XenForo installer escapes the double quote with a backslash if it's used in your database password, even though it is stored in single quotes which prevents installation from taking place. It's caused in library/XenForo/Install/Model/Install.phph on line 392:
And should probably use something like this:
Since there is no reason to escape double quotes in this circumstance.
$lines = '$config[\'' . addslashes($key) . '\'][\'' . addslashes($subKey) . '\'] = \'' . addslashes($subValue) . '\';';
$str = str_replace('\'', '\\\'', str_replace('\\', '\\\\', $str));