I had a bitch JR that used to run upstairs and hump a huge teddy that sat in the corner of the boys room, when she came down she'd be worn out with a bit grin on her chops.
We used to have friends over and you'd hear thud thud thud on the ceiling, friends would ask ''what that'' well..........

Don;t think she was displaying dominance though.........well unless she thought the bear needed to be dominated.

Hi Donny dog forget dominance (there's that terrible word again). As puppies grow they 'practise' a range of behaviours sometimes inappropriately.

When a puppy humps, people frequently laugh with with embarrassment, so the puppy repeats the behaviour because it was rewarded with attention.
The best course of action is to either ignore the behaviour or to distract the puppy with a toy (a squeaky toy often works well ).

My dog Bonnie would use to do this when she got very excited when she was younger, she would try humping our leg or her lead etc.

When we recently moved house though we found at one point she had started doing this again and more regularly and would grab and lick our legs. But after maybe a month or so she pretty much stopped doing this, so we started to think that maybe she was doing this to try and relieve some of the stress she might of had from us moving house and living in a completly new place.

I don't think neither of these occasions were due to her wanting to dominate. But I have also heard that dogs will sometimes do this to show their dominance towards another dog etc.