I've searched around, and only found solutions for Chrome to allow it to be pinned to Docky. Nothing about Firefox. I assume it's the same principle, but I don't know what the StartupWMClass should be. Can someone help me out with this? It's not crucial, but it's nice to have one pinned icon on Docky.
You can perform simple, just by clicking and dragging the Firefox icon to Docky bar or simply when you run firefox and its icon appears on Docky clicking the right button on firefox in Docky and the menu displayed triggering option to fix the Docky, simple as that.