Try this

• http://kb.mozillazine.org/Mozilla_Suite_:_Issues_:_Sound
• https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues

Thank-you. Spent a fair amount of time going through all of this. Nothing made any difference whatsover.

it happen to all the video websites or particular website

This is the advice I got for a similar problem I have with Vimeo (playing with sound but no video) ...

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

You can check for problems with current Flash plugin versions and try these:

   disable a possible RealPlayer Browser Record Plugin extension for Firefox and update the RealPlayer if installed
   disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)
   disable hardware acceleration in the Flash plugin 

   http://kb.mozillazine.org/Flash#Troubleshooting

So --- I spent the day going through the process outlined end-to-end to find that the so called "solution" is the same solution we end up with each and every time we have these problems occuring with hardware acceleration after an FF Update.

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems > Turn off hardware acceleration > Upgrade your graphics drivers to use hardware acceleration and WebGL > Search for and install new graphics drivers > Graphics drivers are all up-to-date and haven't changed since way before the last FF ...

I quote FF "I still have problems with my graphics card in Firefox" "Unfortunately, due to the wide range of possible driver, video card and operating system combinations, hardware acceleration or 3D web graphics (WebGL) may still not work for you in Firefox. In these instances you fix the problems by disabling hardware acceleration and WebGL."

Well, disabling WebGL the problems still exist ...

So the final advice from FF is FIREFOX > OPTIONS > ADVANCED PANEL > GENERAL TAB > Uncheck Use hardware acceleration where available?????

What, FF considers this a solution?????

What, "Uncheck Use hardware acceleration where available" because it was checked BEFORE and now hardware acceleration no longer works AFTER?????

This is a solution?????

Give me a break!!!!!

And NO, I'm NOT being rude. I'm angry that yet again FF fails to automatically crosscheck this within the update/new version install process to advise us at the end of the process that FF has disabled hardware acceleration because it is no longer supported on my set-up.

Now wouldn't that be a r-e-a-l solution?????

I'm amazed that each time these type of problems arise we get the same advice time-and-again to go through this exceedingly manual process of due-diligence checks-and-balances to figure out what it is that we have as ad-ons that supposedly now clash with changes that FF have made to the browser.

Everything is provided to FF with the post yet we are expected to check in SafeMode everything that was passed compatible when FF was updated.

It all comes across a bit lazy I have to say - no disrespect intended to some at FF who will no doubt come back to "slap my wrist", telling me not to be "rude", "refrain from using so many ????? together", telling me yet again "the problem is with your plugins" - especially when history shows us that such checks I'm asked to make "after the event" often do not resolve the problem, more so given that the last FF Update validated all of them, switch off those that weren't and checks on them since show that all are the latest up-to-date without any changes being made to them by me . Then the problem gets resolved by someone else on the forum basically beta testing what should have been checked-out thoroughly by FF in the first place.

Sorry to go on a bit of a rant-and-rage B-U-T we are not getting these repeated problems withe other browsers which we are getting more and more frequently with FF.

Never mind. I'll go through this rigmarole of checks yet AGAIN, no doubt then having to put up with the same sequence of threads from the likes of Morbus re the Plugin-container fiasco "Nothing to do with this [whatever we put forward it might be]. Try flash [or this or that or something else]. Uninstall it and reinstall it. Make sure it's up to date too.", like we're a bunch of morans who don't have the dummy sense to check these things out thoroughly before we go asking for help on the FF Forum.

"Let's blame the add-ons that have nothing to do with FF" Nowt has changed on that front since 08/2010.

Still, what can we really expect from a free browser? A browser that works?????

I hate IE --- but at least it isn't failling over with hardware acceleration issues every few updates!!!!!

THE PROBLEM ISN'T SOLVED --- IT'S "AVOIDED"!!!!!