Hello,

Try Firefox Safe Mode to see if the problem goes away. Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• You can open Firefox 4.0+ in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut.
• Or open the Help menu and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Once you get the pop-up, just select "'Start in Safe Mode"

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.

Thank you.

Started Firefox in safe mode, no sound on any of the youtube videos I selected. Just to make sure, I copy/pasted one of the links to IE and I had perfect audio.

Did you check the volume setting in the player?

Try to delete the webappsstore.sqlite file to remove all local storage.
Otherwise local storage can only be cleared if you use Clear Recent History (Ctrl+Shift+Delete) to remove all cookies (i.e. time range is everything)

You can check if DOM Storage is enabled.

• http://kb.mozillazine.org/dom.storage.enabled

>> Did you check the volume setting in the player?

Yes, it's set at full volume. I can hear a static sound based on how high the volume is set, but no actual audio.

>>Try to delete the webappsstore.sqlite file to remove all local storage. Otherwise local storage can only be cleared if you use Clear Recent History (Ctrl+Shift+Delete) to remove all cookies (i.e. time range is everything)

Restarted firefox, hit ctrl+shift+delete, made sure ALL of the check boxes were marked and the time frame was set to Everything. Didn't resolve the issue.

>> You can check if DOM Storage is enabled.

Dom.storage.enabled is set to true. Set it to false, re-ran the above steps to clear all cache/cookies/storage, then tried again. Still not able to hear anything on youtube. Reset dom.storage.enabled back to true.

Does anyone have a fix for this yet? I am running Firefox 24.0 . Have tried all above . Running latest flash and all other addons up to date. I have windows sounds and things like iPlayer work fine - but youtube no sound.

on my youtube screen in the lower left there is an icon for the sound and it is marked with an x on the right side ???

Yes there is! I can hear sound using IE and there is no x on youtube screen there. So what do I do?

I copied this from a thread on Adobe's forum:

http://forums.adobe.com/message/5735126#5735126
sound not working on youtube

Ortho_Fan,
Oct 4, 2013 10:04 AM   in reply to chaleegeorge

I've see this identical issue posted on other help forums.  Seems that YouTube, itself, is having some issues. 

I just tried a video, and there was no sound.  Then, I noticed that there was an "X" next to the speaker icon. I hovered the cursor over the speaker, clicked on the slider, and moved the slider all the way to the right, and BAM, normal volume again.

From what I can tell, YouTube has set Muted Volume as the default.

Dont know if it is the correct thread,but when i open my pc and then firefox the adobe flash player sounds in the mixer are muted everytime and i have to unmute it when i open firefox.Is there a fix about this?

Thanks in advance.

No, it's not the mute problem that they're currently having.

When I checked the issue originally, audio is enabled and mute is not turned on in Youtube.

I do know about the mute issue and have seen it within IE, this pre-dates that issue.

uptheirons (and anyone else having Flash audio problems on YouTube):

If the problem is muted sound in YouTube videos, this is a YouTube issue that's affecting Chrome and other browsers, as well as Firefox. See this post on Google's forum: http://productforums.google.com/forum/#!category-topic/youtube/report-a-technical-issue/ETfCgHO4MhU

If you're having a different issue, please ask a new question: https://support.mozilla.org/en-US/questions/new

rapozd2234,

I'm sorry to hear that your original problem (intermittent sound problem on YouTube) is still not solved. The best I can suggest is to

1. Try the other solutions in Fix common audio and video issues
2. Reset Firefox using the steps here: Refresh Firefox - reset add-ons and settings

Did you check the volume setting for the plugin-container in the volume mixer via its icon on the Windows Task bar (notification area)?

uptheirons created a thread here: [/questions/973475]

I am using Firefox 27 with YouTube HTML5 beta, and some videos have no sound. For example: http://www.youtube.com/watch?v=FdXh7wtlpI8 Some other videos do work, such as http://www.youtube.com/watch?v=iD9g6PvNOF4

Disabling the HTML5 option, the Flash option does work well.

You can try to right-click an HTML5 video and open the controls if they do not appear automatically and check the volume setting in the built-in HTML5 media player.

Issue appears to be specific to flash. When I set my defaults to HTML5, any video that launches via HTML 5 works fine in Firefox. It's only when the video tries to launch via Flash that I had problems.

I went through and uninstalled the flash plug-in and removed flash from the PC, then did a clean reinstall. Whatever the problem was went away with a new install of flash.

For me the issue was only with HTML5, never with Flash. However YouTube is not showing the mentioned videos in HTML anymore.

I had the same problem on a Windows computer. What I found was that a process was still running after I'd closed Firefox. So when I re-opened Firefox the failing process was still in control.

This has typically happened to me when I unplug the headphones and want to hear from the speaker.

The quick way to tell if you have this problem is to hold down shift whilst starting Firefox (safe mode). It will then report that Firefox is still running.

To fix the problem go into Task Manager (Ctrl-Alt-Del) and close the firefox.exe process.