This is a series of mockups, done by Mozilla UI designer Alex Faaborg, showing what a quick-command interface could look like in Firefox (jumping between tabs, searching, tagging); heavily inspired by the OS X app Quicksilver:
Here are some ideas I’ve had about how several different Firefox features could be designed using a graphical keyboard user interface. Please note that these are all only conceptual mockups, and we currently have no official plans to implement these features for Firefox 3 (although, we may at some point release a prototype extension through Mozilla Labs). If you are an extension developer and are interested in contributing to a project like this, please email me or leave a note in the comments.
All of these mockups show interfaces that are entirely keyboard driven. A keyboard shortcut launches the UI, and the UI is later dismissed by either selecting an item using the arrow keys and hitting enter, or by hitting escape. These interfaces are all modal, and when invoked they occupy large amounts of space on the screen.