Is the site update to handle FF57 protocols? If not then it probably won't work with FF57. Does that happen with other Browsers?

Sounds like a message from Flowplayer that is used on some websites.

Install Adobe Flash the Plugin version. https://get.adobe.com/flashplayer/

Make sure you deselect the "Optional offers", so you don't get extra software that you may not want,

I got the most updated version of adobe flash. and on Chrome I can watch those videos. The sites are www.ynet.co.il and www.sport5.co.il. Any idea?

Can Someone help me?

I can watch them fine, even in Private Browsing.

Update your Video Card Drivers as sites use HTML5 to display video content.

Please : https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer and https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles then https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

Please let us know if this solved your issue or if need further assistance.

See also:

• https://www.google.com/search?q=hlsjs:+unsupported+video

Thank you, it was my adblocker extentions