To this day, this appears to be the best key binding extension for Firefox and other Mozilla (and Mozilla-like) applications. Even the Mozilla wiki recommends using it.
The original add-on by Dorando can be found at http://mozilla.dorando.at/readme.html. This version is functionally equivalent to the original, but compatible with newer versions of Firefox (but not the newest, post-XUL Firefox versions), Thunderbird, and SeaMonkey and with Pale Moon.
If you have questions about how to set things up, please check out the original forum page at http://forums.mozillazine.org/viewtopic.php?t=72994.
Directions to use:
Known Issues:
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