Websites don't play any sound, despite sound being turned on

I was watching some videos last night, without having any issues. This morning however, when I got up and wanted to play a video, I had no sound. I thought that just that video had no sound, perhaps. So I went to a different website to check a video which should have sound, but it was mute as well. Then I went to see if maybe the sound on my PC is muted, however the Mixer is turned up and I'm getting sound from all other sources. When I play something that should have sound, the Mixer also gives off no sign of sound being played from Firefox, so it's not like I'm just not hearing the sound. I'm using a 64-Bit Win7 and Firefox 59.0.2