In Chrome, you can adjust the settings for Flash for any specific site. It's possible to enable Flash selectively for firecalc.com, which I've done and confirmed that it works. So, for now at least, I can see the graph on the Investigate page.
However, I believe that this will only work for another few weeks. As of January, it's my understanding that Flash support in Chrome will be dropped entirely, with no way to selectively enable it for any site.
I'd like to add my voice to the chorus of requests for updating FIRECalc to work fully without any reliance on Flash. I have a programming background, so I would be willing to volunteer to help with this. In my prior w*rking life, I did extensive website programming using both Javascript and Flash (Actionscript).