I think I found a bug in the way the plugin redirects. When I go to domain.com/wp-admin/
I get redirected to http://domain.com/wp-login.php?redirect_to=http%3A%2F%2Fdomain.com%2Fwp-admin%2F&reauth=1
Now after I signed I with BrowserID I would get redirected to http://domain.com/%2Fwp-admin%2F or http://domain.com/http%3A%2F%2Fdomain.com%2Fwp-admin%2F both ways get 404-errors.
The bug seems to be fixed by adding urldecode() to the redirect_to.
$redirect_to = urldecode($_REQUEST['redirect_to']);
But, I'm not sure this is a good fix, because the PHP manual says to not call it on $_REQUEST.(http://php.net/manual/en/function.urldecode.php)