I haven't posted anything in this category for a while, but I recently found an extension for Thunderbird that has really made my day. I've noticed for a while that re-filing messages is too mouse-oriented for my tastes, and have hoped to find a solution.
You see, I'm a keyboard-oriented person. I use emacs as my preferred text editor, but even when I use Word I learn all the keyboard shortcuts, and customize the interface to add more shortcuts so I can do as much as possible from the keyboard. I know the keyboard shortcuts for most of the programs I use regularly, and have little trouble keeping them straight between different programs.
I often say "Bill (meaning Microsoft) thinks people feel productive when they're moving the mouse, and he wants you to feel productive, so he makes sure you have to move the mouse to get anything done." The Mac has unfortunately followed in this direction more and more recently with many monologue boxes (my term for a confirmation window with only one choice.) And too many of the dialogue boxes won't let you tab to a different choice: you have to move the mouse. I thought this went against usability guidelines, but it increases nonetheless.
So anyway, back to Thunderbird. In order to refile messages in off-the-shelf Thunderbird, you can either navigate menus manually, or drag the message to a folder. If you have a large folder tree (as I do), this can be a serious hassle. I haven't figured out how to invoke the menu tree from the keyboard, since the menu is hierarchical, and AFAICT you can only add a shortcut for a leaf of the menu hierarchy. That means invoking the menubar (minimum 5 keystrokes or a mouse movement) or a context menu (mouse movement) then navigating the menus (mouse movement at each level, sub-menus might be on the right or the left; keyboard requires moving up and down with arrow keys, since individual menu items don't have live shortcuts).
Steve Putz's mail reader, Babar (only available in the version of Smalltalk that was used at PARC; the user community never exceeded 50) had a short menu of the most recently used folders that you could reach quickly for filing or visiting. The other alternative is a quick textual search from the keyboard. The Emacs front-end for mh (which I still use regularly to peruse my filtered junk mail) supports this.
Now there's a new (first release was in May) extension for Thunderbird that supports filing from the keyboard. It's called Nostalgy, and it was written by Alain Frisch. Hit a key: "s" (for save?) to refile, "c" to copy, and you can then type a regular expression while the applicable list is narrowed down as you type. And the most recently used folder is immediately accessible by capitalizing the command key, so filing to the same folder you just used (which is quite common) is just "S".