After a recent update, certain websites (like Youtube) leak script that remains even after the tab is closed, until Firefox is closed. When one of these websites is accessed for the first time, a second tab opens and quickly closes, as if a popup was blocked. One way I can observe this behaviour is that the NoScript extension will detect script for that website on ALL tabs, even blank ones, with the "(sidebar?)" annotation. With Youtube I managed to prevent this by disabling Service Workers in about:config, but for example with tenor.com the behaviour continues to occur even then. Websites I observed this behaviour on so far: youtube.com (until Service Workers were disabled) tenor.com nami.news Is this a bug? I have also observed the same behaviour on a different PC for Youtube until I disabled Service Workers on that installation. What should I do?