If you wanted pixel-perfect it was a fucking nightmare. Literally doubled your work time just to add WinIE compatibility. This was in the IE5/6/7 era.
Speaking of JS... all this was made worse because there were NO good JS libraries at the time to make things easier. Debugging consisted of alerts. Eventually, Prototype (and later Jquery) were literally godsends, and there was some JS lib (forgot the name) which added a reasonable debugger (this was before browsers themselves had reasonably good integrated debuggers!)
Chrome is not like that. The same rendering engine exists on Linux, Windows and Mac, and it has an open-source highly-compatible version, Chromium.
Not originally it wasn’t. The UNIX versions are an interesting relic.
Firebug changed my life when it came out!
But that was probably a bit earlier, since I was off Windows by '98 or '99.