But also, google spent a mountain of money advertising chrome.
I think this factor isn't given enough weight in the shift to Firefox.
At that time, the largest pain point in web development was (by a long shot) browser compatibility.
When developers fell in love with Firefox, they started pushing business requirements away from IE and towards the browser that didn't feel like it was their enemy. Alongside with this there was also massive shift to start taking web standards seriously, which is another area where IE dropped the ball spectacularly
It took a few years, but eventually pointy haired managers got sick of our whining and gave in.
Once Chrome came along with their devtools, improvements quickly escalated between the 2 before Google eventually won out.
I can't recall the exact point in time when my use of Firefox fell off, but it was probably due to the account integrations with Chrome.
Not to mention preferential treatment like the Youtube anti-IE campaign [1]
[1] https://www.theverge.com/2019/5/4/18529381/google-youtube-in...
Chrome was a lot faster and a lot lighter (in the beginning)
That money was also used to increase the user base via drive-by installations, e. g. while installing Adobe Reader you had to deselect the Chrome installation, otherwise you'd find yourself with a new standard browser afterwards.
Neither KDE nor OS X ever shipped their built-in Web Inspector prior to the appearance of Firebug in 2006, and by that point WebKit and Safari were already in full swing. The very first iteration[1] of Web Inspector appeared around the same time as Firebug and was an original contribution by Apple; it wasn't borrowed from KHTML.
1. <https://web.archive.org/web/20070621162114/https://webkit.or...>