Jumpbykey is an extension that allows you to better sort and filter your messages just by hitting a couple of keys.
To activate the sort mode, you can disable all the shortcuts with just a key (es. j for "Junk"), press CTRL-9 (was CTRL-0 in 0.1 version), to exit press ESC. You can enable the "jump-mode" on startup, setting the pref "jumpbykey.enable_on_startup" to true.