If the site is coded to hide the HTML5 player from Firefox, then what can you do? Oh yeah, lie to the site and tell it Firefox is Chrome. Might work, might crash Firefox.

The extension ua-site-switch, which admittedly has a rather confusing interface, can be used to send specific user agent strings to different sites. To find Chrome's UA string you could search for it or load this page in Chrome (the UA is in red):

https://jeffersonscher.com/res/jstest.php

https://addons.mozilla.org/firefox/addon/ua-site-switch/

You can find the latest Flash player versions for Firefox on this page:

• http://www.adobe.com/special/products/flashplayer/fp_distribution3.html

Works for me with the HTML5 media player

• https://www.udemy.com/learn-html5-programming-from-scratch/

I see the WebHD.mp4 played via a video tag. The file is hosted on cloudfront.net, so make sure that you aren't blocking content.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

jscher 2000, I'll give that a try and see what happens.

cor-el, the whole point is that I do NOT want Flash installed period.

ua-site-switch does work to spoof a different browser but it doesn't help with udemy.com.

Whatever method they are using to wrap the video always kicks back to "install Flash Plugin".

Looks like at present the best option (Flash is dead to me) is to use Chrome or Edge.

It works for me with the built-in HTML5 media player on Linux. I only posted the link to Flash in case you would want to install Flash.

There is an iframe that is created by processing the code in this div that is part of the page code. I can't right-click the player area, but it looks like JWPlayer code and there is a video tag in the page code.

<div class="col-lg-8 col-md-7" data-purpose="introduction-video">
                                    <div class="slp-promo-asset ud-jwplayer-communicator"
                         data-playerhtml='            <iframe id="2375582"
                    src="https://www.udemy.com/embed/video/E0EYdltXTX4T/?params%5Bvars%5D%5Bplaylist%5D%5B0%5D%5Bimage%5D=https%3A%2F%2Fdujk9xa5fr1wz.cloudfront.net%2Fcourse%2F750x422%2F41295_dd3f_5.jpg&params%5BtrackVideoPlay%5D=true"
                    width="100%"
                    height="100%"
                    frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen
                    style="background: black;">
            </iframe>
        '>

• https://www.udemy.com/staticx/udemy/js/jq/ud.jwplayer.communicator.js

cor-el, if I link direct to the video I can get it to function as well. However, udemy.com support states that Firefox is not compatible, which I presume has something to do with how they are wrapping/embedding the video.

Does it work for you on this page?

• https://www.udemy.com/learn-html5-programming-from-scratch/

Can you post as link that doesn't require logging in that doesn't work?

cor-el that's the issue. The non-functioning must use flash seems to only occur on videos requiring a log in.

Conversing with udemy support as they are also puzzled that html5 intro videos play and if I copy the url to a course video from chrome or edge the video also plays in Firefox.

So its doubtful the issue is that Firefox does NOT support HTML5 video.

Worked with udemy support to track down the problem.

Udemy has fixed the bug that kept kicking Firefox to the "requires Flash" dead end.