It isn't the webrep as that doesn't really care where you put it (well I don't believe so), yes it will have a default location where it is displayed now. But you should be able to drag it to another location in the Customise function in firefox.
Though I don't know if firefox would allow you to place it in the same location as the tabs, but I have just done that and it allowed it (I also changed it to Tabs on top, which personally I don't like) so we will see if it sticks on a firefox restart.