Is there a way to automatically expand all "older posts" on a Facebook wall at once? I'm using Firefox if it matters.
As you are using Firefox you can install the Better Facebook! Firefox Add-on.
The add-on provides numerous features/enhancements. One of these being
This should provide you with the functionality that your require.
You can actually install this on Firefox, Chrome, Safari & Opera. The website for further information can be found here
You can also run this script in the console.
And as of 30/04/2013, the id has changed. The valid code is now: