Hindi Devanagari font issue

I signed up on pronunciator.com and was attempting to start their Hindi courses, however none of the browsers I use will display the Devanagari font used in the lessons (which are Flash-based). I've tried Safari, Firefox and Chrome, tweaked every imaginable setting and all I get are blank boxes (or asterisks if I click on them). I'm able to use the site with all the browsers I have on my Windows 10 partition (although I needed to install East Asian language support software first), but am having zero luck getting it to work on the Mac (2011 iMac, El Cap). I'll enclose a screenshot of what I'm seeing. I sent a ticket to their support and the response was

"I found this on a forum just now: "Devanagari seems to work if you use Apple's Kohinoor font."

I hope that helps!" Well, I have that font, and have tried disabling the other Devanagari fonts, restored standard fonts, zapped PRAM, etc.

Any help appreciated :-)