janiehub, have you ruled out the basics? Sound can stop for several reasons, including: * the website has its own keyboard shortcut for muting its audio, which might have been inadvertently pressed. * the tab has been muted in Firefox, perhaps by the accidental clicking of a tab mute button, or the pressing of ctrl+M. * the Firefox application has become muted in either the OS volume mixer, or the sound card's own software settings. In Windows you might be able to check the volume mixer by looking for a speakers icon in the bottom right notification area, right-clicking it and seeing if there is an 'Open Volume mixer' option.