If you mean a basic calculator in the URL bar, Firefox has that too (also a simple units converter) but off by default. They do that because people use search

If you mean a basic calculator in the URL bar, Firefox has that too (also a simple units converter) but off by default. They do that because people use search engines for that kind of stuff. The implementation (at least the Firefox one) is quite simple. browser.urlbar.suggest.calculator browser.urlbar.unitConversion.enabled