Hmmmm, back in those days (and earlier), I recall that I only switched to Win 98 (from Win 3.11 for Workgroups) because I was concerned about Y2K issues, and there were more mitigation measures available for Win 98.
However, it was also at about that time that newer versions of Netscape (my browser on the WFWG PC) stopped supporting that Windows version, and to continue to use a newer NS, I would have had to move to at least Win 95 anyway.
Bear in mind that although I stayed behind the curve for my OWN PCs, I operated a computer store for 15 years including that period, so I had in-house access to each Windows version as it came along, on the clone PCs which I serviced and sold.
I did not try Opera until its version 10 and 11, and that was MUCH more recently, because a Win 2000 PC I on which I wanted to keep browsing the web would not work with FireFox 14, I think it was, and its own IE6 (max for Win2K) was beginning to not display certain sites properly.
Later, on that same PC, I determined that Win2K does accept FireFox 10 and the 10 esr series.
I also did encounter browsers where we had several columns of root-level bookmarks, but do not recall which.
IE8, for example (and which I still use part-time) has a single scrolling column, but the header is locked as I prefer - and wish to make happen with a current Mozilla-based browser.
I do not believe that I ever used the Mozilla suite, and neither did I use early SeaMonkey, nor Phoenix/FireBird, so it had to be Netscape (and of course IE5 thru IE8) where I experienced the Bookmarks Menu presentation which I prefer.
= = = = = = =
And a piece of trivia which most folks do not know (as they never gave Windows Vista a fair chance) is that my tests last night (of FireFox 1.0 and 1.5 Portable editions) were performed on a Windows Vista 32-bit PC, and it accepted those old FireFoxes just fine, though I had originally used those two browsers on Win 98SE, where they also worked properly at the time.
EDIT - UPDATE :
I just found a portable edition of Netscape 9.0.0.6 (though I think that the last version which I had originally used was 7.something), and installed it to the Vista PC, and it works fine, but still has the VHS (vanishing header syndrome).
= = = = = = =
BTW, this last group of posts in the current thread is better suited for THIS linked thread :
»
[Firefox] Bookmarks Menu Header - How to Prevent Scrolling 
