https://marco.org/2008/06/18/me-have-you-ever-written-an-extension-for
Me:
Have you ever written an extension for [Firefox]? [it sucks, etc.]
The only extension I’ve tried writing was actually for Firefox 1.0. The only documentation at the time was the bug-me-not example application. Ugh.
Me too! I wrote the Clusty Toolbar, one of the first official Firefox search toolbars. (We beat Google by a few months, but A9 beat us by a week.) This was about a month before the 1.0 release (fall of 2004) when the big internet companies weren’t taking Firefox seriously yet.
You’re right - there was absolutely no documentation. The only way to figure out how to make extensions was to peek at the source of other extensions (since they’re just renamed .zip files).