I am using the latest version of High Sierra (10.13.3) on a mid 2011 27" iMac. I find that the "mute" action for tabs on the Safari browser sometimes doesn't work. When it is boring, I can hover my mouse over a tab that has sound and see a little speaker that I can click to mute/unmute the sound on that table. Very often, however, the little speaker icon is not present on the tabs and thus I can't mute an individual tab. Anyone else have this problem - know of a fix?