There are a few, but all the ones worth using are built on top of Firefox or Chrome (Chromium). A browser rendering engine is a big, complicated piece of work that has to constantly evolve to keep up with standards. Most of the problems are in the rest of the browser; although Google’s upcoming change to prevent ad blockers may deep in the Chromium engine. Search engines have always been a large endeavour. If you want to index and search everything on the ever growing WWW it’s going to cost millions. Once you’ve pulled that off try doing well and fighting the search engine spammers at the same time.