Keeping Firefox to Dock fails, Exec= empty

Hi all, really enjoying the simplicity of this project.

One thing I just ran into is that I put Firefox pinned to the dock, but it won't launch when I open it from there. Other applications I tried seem to work fine. But for some reason, Firefox will launch just fine from the terminal, or from the System menu, but not from the dock.

Also, is there some way to rearrange the items in the dock without removing them all and then adding them again?

Thanks!