I've just discovered a way to solve this second problem, which I'm posting in case others didn't know about it. To move between folders without opening every folder in between:
- Move to the folder selection tree.
- Press ctrl+space to deselect the current folder.
- Rather than using the up and down arrows to find the desired folder, use ctrl+up and ctrl+down, respectively. You can of course keep your finger on the control key. Notice that Thunderbird does not open each folder.
- When you reach the desired folder, press ctrl+space to select it. Thunderbird opens the selected folder.
There is also the Nostalgy extension, which, among other keyboard productivity enhancements, allows you to jump to a folder by typing all or part of its name. However, I use Thunderbird 3 nightlies and there have been a few compatibility issues recently. Also, Nostalgy overrides the functionality in the quick search bar and it makes the quick search menu inaccessible, so I don't use it anymore. (I should really report a bug, but I can't quite figure out what's going on.)