I could reproduce it, and will try to come up with a fix.

Meanwhile, a simpler workaround using the option "Drag within/between groups using right mouse button":

When the console window closes, right click and drag the second Firefox button out of the taskbar. Then, drag the button onto the pinned item.

Have you tried to manually install to the Program Files folder by running the setup as administrator?

It should work. The only limitation I can think of is that you'll have to remember to launch the uninstaller as administrator, too.

Seems like there's nothing I can do about it.

If you have ideas, add a comment below.

Seems like there's nothing I can do about it.

If you have ideas, add a comment below.

Please see my comment here:

http://rammichael.com/7-taskbar-tweaker/comment-page-16#comment-3428

Taskbar items -> Hovering -> Nothing.