Who should be allowed to add stories to the product backlog?

What is the best practice for that prevents the backlog from becoming a mess, but also maintaining developer productivity

Who should we allow to add stories to the product backlog? And how do you make sure these stories meet certain requirements?

For example I find a few small css bugs during the development of Feature X. Should I then as a developer be allowed to add a story describing the bugs to the bottom of the backlog? Or should I discuss it with the product owner?

Having all ideas/bugs go through the product owner sounds like possible bottleneck.