Force the HTML Uploader

If you need to force users to use the HTML uploader, you can do so with this

add_filter( 'flash_uploader', 'force_html_uploader' );
function force_html_uploader( $flash ) {
	remove_action('post-html-upload-ui', 'media_upload_html_bypass' );
	return false;
}

The remove_action() portion removes the “You are using the Browser uploader” text. The rest is what forces the flash setting to be false.