I usually have a number of tabs open for different sites in Firefox. The left most one is usually the one for a certain car forum I visit frequently. Firefox indicates on each tab, an icon and some text, to indicate the web site.
Today, that first tab had a the symbol for a speaker with a line through it, indicating the audio was turned off on the extreme right of the tab. None of the other tabs had the symbol. Closing the tab and reopening cleared the symbol. Did it have some meaning?