The link for the IE Developer Toolbar in the original article carries a date of September 19, 2005 in the URL. Which makes sense, because it was demonstrated at PDC 2005, which was the previous week.
Note also that the release notes for Firebug v0.2 state: "This is a very early release - the code is only a few days old." Whereas the IE Developer Toolbar probably began a couple of months before its first release. So even by looking at the first mention on the web, we're comparing a days-old Firebug to a fairly-complete IE Developer Toolbar.
Link: http://betanews.com/2005/09/19/microsoft-issues-ie-developer...
Note also that the release notes for Firebug v0.2 state: "This is a very early release - the code is only a few days old." Whereas the IE Developer Toolbar probably began a couple of months before its first release. So even by looking at the first mention on the web, we're comparing a days-old Firebug to a fairly-complete IE Developer Toolbar.