Things instantly became real when firebug for IE came out. To me that one tool made a front end web development career a viable option. Do y'all remember JS before Firebug? ouch
Most people debugged with alerts or document.write-ing in the page. The "wokest" were aware of Venkman (Moz/FF), Script Editor (IE) and the Visual Studio IE integration (also IE), all of which were pretty much just JS debuggers.
Venkman worked the best but the UX was a horrendous mess, SE and VS were less visually messy but (likely due to IE) frequently got lost entirely and were completely unable to debug the JS toplevel ("and "modules" were not really a thing back then, so much of your code would live in the JS toplevel).
This was also the epoch of Drip, an IE webview which would just reload a page over and over checking for IE's infamous DOM leaks.
God I so don't miss it.
Firebug was definitely a pivotal moment, a complete perspective shift for the field.
Firebug was revolutionary not only for the console but the inspect tool was very needed as layouts and CSS progressed where outputs weren't enough.
In theory that could have been caught by a good jslint/syntax checker but those were a few years in the future too. Early, JS development really sucked, its only slightly better today..
I recall a dramatic bug where, in 2012, I rolled out a new version of a web GUI with some JS mixed in it to an intranet audience of IE 7 and Firefox users. It initially looked good, but then reports came in that IE users couldn't use one of the buttons. After much debugging and confusion, it turned out that there was a trailing comma at the end of an array literal (i.e. `[1,2,3,]` instead of `[1,2,3]`). Firefox accepted that, but IE 7 didn't. (I think IE 8 added support for trailing commas.)