I am running Linux Mint Mate 18.3 on a fairly recent Dell i5 processor with 8 GB ram. When I try to log on to Sling TV, https://watch.sling.com/browse/my-tv, I get the message: "Sling TV is not supported on Ubuntu browsers" (see screen capture). However, if I use Chrome or a couple of other browsers the site comes right up and plays any video I chose. I've tried this on several of our computers running various recent Linux Mint builds and get the same result. So the issue is apparently with Firefox, not Linux. I've tried disabling any extensions that might block access (adblock, no script, ghostery, etc.) but that doesn't make any difference. Firefox does work with most other streaming services - Netflix, Amazon, Google, etc. Widevine is installed. Any suggestions?