Does this issue occur only on twitch.tv or does it occur on all websites with video/audio content?

If this issue is exclusive only to the Twitch website, please try clearing your browser's cache and cookies. Sometimes, these cache and cookies become corrupt and prevent a website from operating properly. Removing the corrupt files will force Firefox to download new files that are not corrupt.

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• Delete browsing, search and download history on Firefox

Firefox 42 does have a new "mute" button on a tab which is playing audio, but I think it's just on/off and doesn't affect volume.

If you check the Windows 7 volume mixer while playing the media, can you tell whether the sound is outputting through Firefox or through a plugin? To open the mixer, click the volume icon in the notification/system tray area, then click Mixer. This should help distinguish between "native" playback and plugin playback at the system level. I've attached an old screen shot as an example.

So I went into the mixer to see check to see if there was any sound, and I found out that it had been completely muted somehow. Now it works fine, thank you!

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