I have Firefox as one of my favorites. When I open Firefox, the little "running dot" in the favorites bar is missing. So when I click the icon to return to the open instance, another instance opens instead.
When I remove Firefox as one of my Favorites, the orange dot appears, and clicking the icon returns me to the running instance.
I know I can go to "Activities" and find the window, but I'm in the habit of using the bar. But I'm wondering what would cause an app not to show a running dot. It may be just a Firefox problem, but the fact it shows when not a favorite suggests it might be an Ubuntu problem.
Edit: Running Ubuntu 22.04 LTS, Firefox 100
Best Answer
Not really an answer, but there's a bug 1972545 here and a collection of other bugs on a similar effect.
One suggestion is that it may be that these are snaps: the snap has updated behind the scenes but Firefox (or other app) has not yet been restarted. It is claimed that restarting Firefox will fix it (until the next time).