The speed at which a web page renders to the screen is based on a whole group of factors. With everything being equal, which is next to impossible by the way, the rendering engine used in the browser manufacturer is the key component of how a page displays, both layout and speed.
The Chrome engine, which is currently called Blink was developed in C++ and in terms of rendering engines is a relatively new one. It is well written and includes it own set of very good built in development tools. Chrome is also one of the more popular browsers as it has been optimized for the Google SEO tools available through Google.
Firefox uses the Gecko rendering engine and was very popular a few years ago but over the last couple of years has fallen from grace with issues on security and lack of updates to the engine in support of the many changes that are occurring with the web development languages. It too is written in C++ but an older version of the code and has not gone through the updates that it should have to keep up with the changes. It is still popular but losing ground with every passing month.
Now getting back to your question. The speed at which a page is translated depends on a combination of the connection, available threads in the processor, the rendering engine, the complexity of the page, the structure of the page and how well the rules (web standards) have been followed in the development of the page. Most people are not aware of this last one but it makes a big difference because that determines how many things on the page need to be tweaked, by the engine and interpreters to display correctly. When you start adding special code for IE browsers, conditionals in the head section of the pages, loading from a dynamic source, etc. That all slows down page loads.
Items running in the background of the terminal can also have an impact on how the page loads. There is so much background junk running in Windows that at times I am surprised those terminals function at all. It is amazing all the processes that are going on in Windows at times. The Macintosh, though a very good computer, has many of the same issues with background processes. They are handled a little better based on the the limited number of peripherals and drivers needed to make the Mac function, but they are still there.
Even multiple link files, i.e. CSS files, JavaScript files, PHP includes, etc can add 200 ms per item to a page load. That does not sound like much but in computer terms a second is a lifetime.
So as you can see, the rendering engine does make a difference, but it is not the only difference. Different engines require different processes across the hardware, how well those processes are managed by the hardware and the software has a big impact.
Even things as simple as the type of connection, wireless / wired, secure, unsecured, fixed IP, dynamic IP, gateway, etc. All make a difference. And by the way, just because you are using the same terminal on the same connection type, does not mean that those things are equal minute to minute. Like everything with this technology those dynamic connections can fluctuate with (QOS) "Quality of Service" from one moment to the next.
And on top of all of those constantly changing dynamics..... the languages we use are constantly being updated and changed.
So as you can see, that is why so many developers are bald. It is from us pulling our hair out trying to constantly deal with a changing environment. But we would not have it any other way..... that is what presents the challenge that keeps us coming back for one more go at trying to get it perfect.
By the way, few if any of us...... ever do! But we will keep trying.
