So, so tired of the "hot take" that having a single browser engine implementation is good, and there is no value to having multiple implementations of a standard. I have a little story to tell about this.
In the late 90s, I worked for a company called Vectiv. There isn't much info on the web (the name has been used by other companies in the meantime), this old press release is one of the few I can find.
Vectiv was a web-based service for commercial real estate departments doing site selection. This was pretty revolutionary at the time, as the state-of-the-art for most of these was to buy a bunch of paper maps and put them up on the walls, using push-pins to keep track of current and possible store locations.
The story of Vectiv is interesting on its own, but the relevant bit to this story is that it was written for and tested exclusively in IE 5.5 for Windows, as was the style at the time. The once-dominant Netscape browser had plummeted to negligible market share, and was struggling to rewrite Netscape 6 to be based on the open-source Mozilla Suite.
Around this time, Apple was starting to have a resurgence. Steve Jobs had returned, and the candy-colored iMac was proving to be successful. Apple was planning to launch official stores, and the head of their real estate department was a board member of Vectiv, so we managed to land our first deal - a pilot project with Apple's nascent real estate department.
We picked up a few iMacs around the office for testing, and immediately hit a snag - Steve had ordered that everyone in the company, real estate dept included, has to use the new Mac OS X. The iMacs that the dept used (and that we tested on) were pretty slow, but serviceable. The real snag was that our product didn't really work on IE for Mac. Like, at all. Pages wouldn't load, and the browser would consistently crash on certain pages.
This was before Safari and its Webkit engine, We started debugging and rewriting bits of the product, and simultaneously talking to Microsoft about our problems. They were responsive, and hopeful the upcoming update would fix some of our problems. Sadly, there were to be no further updates for IE 5 for Mac.
I was something on a Unix fanboy at the time, and had been using early releases of Mozilla Suite on my Solaris workstation, so I knew that our product basically worked with some rough edges (mostly minor things like CSS, with a few less trivial problems around divergent web standards.)
Long story short, our QA manager and myself visited Apple's real estate and test folks, and we settled on using Mozilla 0.6 for the pilot, and corresponding Netscape 6 when it was released (I think we ended up using Netscape 7.1, which I recall being a lot more usable, being based on Mozilla 1.4)
Vectiv had other clients like Dollartree and Quiznos, but getting over that initial pilot hurdle was key to proving that our product worked and had backing from a known brand. Vectiv was VC backed and like many startups caught up in the dot-com crash ran out of runway, although the product was sold and did live on. I did a few consulting gigs setting up local installs for the remaining clients.
Most people reading this probably know the rest of the story - IE stagnated, AOL pulled the plug on Netscape, and Mozilla Suite was reborn as the Firefox browser. With MS moving to Google Chrome's Blink browser engine, Mozilla Firefox's Gecko engine along with Apple Safari's Webkit are the only independent implementations of the various web standards.
(Blink is technically a fork of Webkit, but IE and Netscape were ultimately forks of NCSA Mosaic, I think it's fair to call it independent at this point.)
To be clear: having multiple browser engines didn't ultimately save Vectiv, but Firefox did open the door for Safari and Chrome, as Firefox's Firebug (the predecessor of today's integrated devtools) enticed web developers enough that they made their sites more standards-compliant just so they could have access to nice devtools.
It's easy for me to write a nice narrative of the past, complete with the moral of the story. The future isn't totally certain, but it's clear that the web will continue to play a large role in the world. Let's not (again) back ourselves into a corner and cede all meaningful control over that future.