There is a major factor that kicks in when a browser gets the most market share, particularly >50% of the total, as Win IE did in the 90s and Chrome did a few y

There is a major factor that kicks in when a browser gets the most market share, particularly >50% of the total, as Win IE did in the 90s and Chrome did a few years ago. Because web site developers test their site in the "top" browser, and then maybe other browsers too, becoming the top browser gives you a huge boost in compatibility through no virtue of your own. Every website works in that browser now because website developers make sure they work. This creates a shift among users, who notice that every site works in the top browser, but only 90% work in browser x, and they start shifting to the top browser and often won't even report problems they have with other browsers. The effect is obviously self-reinforcing, and the top browser continues to gain share. The counter-measure to this is standards. With rigorous web standards followed by websites and browsers, if the top browser works, so do all the rest. There isn't much to enforce this though, and there are temptations on all sides not to do the right thing.