https://www-archive.mozilla.org/projects/venkman/
edit: there's a nice write-up of how firebug got started here https://flailingmonkey.com/the-history-of-firebug
Is it, really? The experience of Venkman was horrendous. Not quite as bad as MS’s Script Debugger (I don’t remember venkman crashing multiple times per session, and it was able to debug the toplevel frame), but still just awful all around.
And more relevant, it was nothing special, at least that I remember. It was notable in being a “normal” extension, but that aside it was a pretty standard if not sub-par debugger experience for the time.
But going back to the relevance subject, I don't really think it is worth mentioning. But not because of performance but because it was a fairly different thing. Mostly just a JS debugger with a couple of additional tools and little/no support. Usually you would need a bunch of other scripts such as XRAY [0] and others to reach a functionality somewhat comparable to Firebug.
- modal interface*
- bloat
- dubious** interface labels, like "DOM" (or whatever) to look at the object's property tree
- totally sucked at debugging any part of the Gecko runtime/toolkit code, or anything that wasn't a Web page (including e.g. Firebug's own code)
* This is a misfeature that every browser's built-in devtools copied, and it's completely mystifying. Thanks, Firebug, but I want the script debugger to be separate from the DOM Inspector, so I can have both on screen at the same time (and I want to be able to have multiple inspectors for multiple objects open at the same time, too, for that matter, so I don't have to keep flipping back and forth between them like I'm navigating fullscreen mobile apps and being forced to think through a straw. I don't even use multiple large displays; I use a 13" laptop screen for everything. No idea why all the proponents of large, multi-screen setups don't bristle about this to an even noisier degree.)
** Generous description; "inaccurate" (or just plain "wrong") would be accurate
As for persons, I like the decisions that Hewitt made when he made DOM Inspector before going on to do Firebug. It was like UNIX pipes (incl. that you can string them together to arbitrary lengths), but with dynamic visual inspectors on each side, instead of bytestreams/text. Firebug was not that. It was one step forward, two steps back.