The browser engine gets HTML, parses it, and turns it into an array of pixels. Hopefully without crashing and without any security vulnerabilities. The rest of

The browser engine gets HTML, parses it, and turns it into an array of pixels. Hopefully without crashing and without any security vulnerabilities. The rest of the browser is the UI built around this engine - it reads your URL bar, tells the engine to render the page, and handles things like navigation and bookmarks and saved passwords etc. Browser engines also execute the JavaScript, though I'm pretty sure Servo just does the HTML/CSS rendering. Webpages these days are very heavy which is why parallelism is important (for both the layout engine as well as the JS engine).