When I open Firefox, a second icon appears on my taskbar and I cannot unpin the original as right clicking does not bring up that option.

I have just installed Firefox and was surprised that, when I click on the taskbar icon, another icon appears next to it. When I right click on the second icon, options appearing include to pin (yes, pin, not unpin) this program to taskbar (I tried uploading a screenshot of this but gave up after 10 minutes). Right clicking on the original icon does not give any options at all. Right clicking on all other icons (Outlook, Word, etc.) gives the option to unpin the program from the taskbar. If I left click on the original icon, it opens another instance of Firefox. Left clicking on any of the new Firefox icons in the taskbar gives a thumbnail of the web page(s) currently open. Firefox is the only program that does this. Is it normal?