You can't expand all folders by default. We had this in place long ago, and it slowed things down so much we had to pull it.
But we do have a setting that will get you halfway there.
Go to Settings > Manage Files. Select the option called Double-Clicking Drawer/Folder Expands All Subfolders.
This works just like it sounds. If you double-click a drawer or folder, all of its subfolders will expand. Double-clicking a folder again will collapse it.
This gives you an easy way to fully expand folders when you need it, but doesn't slow the system down.