Thanks for reaching out to us! You should be able to upload multiple files from Safari (it’s working fine from here). The simplest way to select multiple should be to hold down the Command key while clicking the files you want (or here’s an article outlining some alternate ways to select multiple).
If this still isn’t working can you please let us know what happens when you try to select multiple files? Is the issue that you can’t even select more than 1 at a time? Or is it that they won’t load? If they won’t load, it may be that you need at add *.ribbet.com as an exception to any ad-blocking or anti-virus software you have running.
Regards – The Ribbet Team