The first browser I have been using on a daily based was Netscape, in the 90s Later on, I had no choice but use Internet Explorer at a time a large portion of the web was not compatible with other browsers. The revival of the Netscape browser under the Mozilla name brought me back to it. It was more a matter of silently protesting against Microsoft than anything else. When the Firefox browser was released (initially under the name Firebird), I immediately switched to it. This time, the main motivation was the stability, speed and power of the URL bar. Since then, I have always used Firefox, for a few weeks, I have tried to use Opera, Chrome and Vivaldi, but none of these were as good as Firefox, mainly because of the URL bar, if you only remember one word of a URL, whether it is part of the FQDN or the path, you find it in no time.
At this time, I thought I would settle and stick with Firefox for the rest of my life. Then, came the Zen browser, all the power of Firefox, plus the left sidebar for tabs (much better than on top, as this is where the real estate of the screen is since the 16x9 and higher ratio) and a very neat way to open quick preview widows.