You can use some firefox options to both disable the default action which is to paste on clicking the middle-mouse button and also to turn on auto-scrolling.
First - in the Firefox - Preferences - Advance settings ensure you have the following options checked:
- Use Autoscrolling
- Use Smooth scrolling
Then in the Awesome bar type about:config
Search for *autoscrolland double click *general.AutoScroll to change from "false" to "true"
Now search for middlemouse
- middlemouse.contentLoadURL = false
- middlemouse.openNewWindow = false
- middlemouse.paste = false
Then restart firefox
When you middle click you should now see this symbol to scroll:
