If it was a closed source project you'd have to start from scratch every time if you wanted to restart the project.
It is not unheard of that someone tried and abandoned but would probably have achieved their goal by starting from scratch rather that attempting to revive an outdated unmaintained project.
1. This End User License Agreement ("EULA") governs your use ("You") of the browser software in executable form ("Software") and any ancillary services ("Services") provided to You by Vivaldi Technology AS ("Vivaldi") to the exclusion of all other terms and conditions. Source code used in the Software, under open source license agreements, can be obtained at https://vivaldi.com/source.
Edit: Never mind, homepage ads I see. Eh easy enough to close them out..
Then why has Firefox been the 'shit' browser for the better part of a decade now?
Best battery life (usually by a 2-4h difference!) -> use Edge/Safari
Best stability -> use Chrome
Best performance -> use Blink-based browser
Most extensions -> use Firefox (Chrome has 90% of the FF extensions available though)
Hell, Firefox still doesn't have e10s fully working, so one tab takes down the entire browser. Slow sites lock up the UI. Scrolling sometimes still isn't smooth. Plus, Firefox is ugly, especially on mobile. and whilst its admirable they still prop up Gecko, its a substandard rendering engine compared to Webkit, Blink or Trident/EdgeHMTL.
I would gladly switch to Firefox on my dev machine (opening both Photoshop, Visual Studio and Chrome in a 8GB RAM system is a recipe to disaster), if their development tools didn't suck.
Sorry but not everyone thinks in short term personal interest, some prefer to see the internet and web as a collective good that has to be preserved with a long term vision.
I have a lot of criticism of mozilla and firefox but I would not ever advise anyone to use a GAFM (Google, Apple, Facebook, Microsoft) product or service.