Firefox was seriously a better browser, not just "implements standards better". It ran faster, it had tabs (wow!) and at one point it got Firebug which let you have a console INSIDE the browser that showed information you could print with `console.log`, I kid you not.
It was a better browser through and through, maybe because MS slept on IE or maybe not, but in the end it isn't revisionist to say they beat MS's proverbial posterior because the browser was better.
> beat MS's proverbial posterior because the browser was better
not via marketshare. The fact is, only developers (and adjacent) were using firefox. IE, during those days (pre-chrome) was still such a dominant browser that you had to check for IE compatibility.
But today, developers are not checking for firefox compatibility. So, firefox today (and during the firefox heyday) were never truly "beating" IE from a marketshare perspective.
One big feature at the time was Firefox had a built in popup blocker, IE did not. Popup ads were rife towards the backend of the 90's and the internet felt borderline unusable without a blocker.
Firebug was a big reason for webdevs to adopt firefox in the first place. Part of what made chrome succeed is it came out with a pretty robust set of webdev tools right from the get-go.
But also, google spent a mountain of money advertising chrome.