When I right-click the Firefox icon on my taskbar while the program is running, nothing happens. No jumplist, no "pin to taskbar" option, etc. Nothing.
I can manually pin the program by dragging Firefox.exe to the taskbar, and the jumplist works for that icon, but when I open Firefox, it makes a new icon on the taskbar rather than using the one that's already there (as if I'd pinned a shortcut rather than the actual program file).
This is getting rather infuriating, because jumplists have been alternately broken and fixed ever since Firefox 10.
It wouldn't be such a problem if updating Firefox would keep the same icon on my taskbar instead of making it start acting as if I'd pinned a shortcut, forcing me to re-pin it and experience the behavior above.