The following hotkeys are available in the browser preview:

G - Show Coordinates

Shows the position and rotation of the avatar, which can be useful info when positioning your objects. Click on the values to copy them to the clipboard.

L - Asset Browser

Shows a list of all available prefabs with a thumbnail preview of each one. Click on a thumbnail to copy the prefab id to the clipboard.

V - Fly mode

This way you can fly around to get a better overview of your creation.