I think Firefox is supposed to block sounds from websites automatically playing, evidently because people, myself included, find it annoying. I say I think, because it seems to me, and I might be wrong, that this is a recurring promise. It seems like I hear that the next version will have this feature. And the a release or so later I hear the same promise. However as annoying as the sounds are, I find it just as, and probably more annoying that (when working) they only stop you from hearing the sounds. In my observance the much heavier bandwidth using video is still playing without sound. For me the sound should stop because the video never started playing. When the sound is playing, I at least had a clue that necessary bandwidth is being used, and could attempt to locate and stop the offending bandwidth thief.
The reason this is such a problem for me is because I get my news from clicking on rss news feeds, which opens the subject in a browser tab in a different desktop workspace window. So for example, I may click on 10 rss news articles from different news sources of particular interest to me, out if 100 rss summaries, which opens a new tab in my browser on a different desktop workspace. Then when I’m finished I then go to my browser, for a more depth information on those 10 rss feeds of interest to me only to find that they may have, not only already shown a video related to the story I was interested in but also automatically played other videos of things I have no interest in whatsoever. Because for whatever stupid reason, many sites automatically just go from one news video to a another random video. So in addition to all this bandwidth waste, I may want to replay the video connected to the story I was interested in.