As far as I’m aware the default location is to the right of the navigation bar (since avast 9 as far as I’m aware), so if it is enabled then it will be on that bar when you do use it.

There are no user settings in relation to if it should be displayed on the navigation bar, some have tried, but it can’t be moved to a different location. When you close and reopen firefox, it is back to the default location to the right of the navigation bar.

It is no longer the WebRep, but the avast online security (add-on).

EDIT: So it not only has a default location but by your video when enabled, the avast online security will open the navigation bar if you had that deselected.