I will try exing this in a way both tech technically inclined people can understand. I am also using the current Quora page as an example. Assuming all other factors (platform band processing power disk speeds memory and the page being viewed) to be equal(they should be for fairparison) the factors that determine the browsers speed in terms of what is perceived by the user are 1. The Layout engine engine nEach browser has a layout engine under the hood. For example the different browser engines used in browsers aren WebKit Chrome and Safari Gecko Firefox Trident IE Presto Operan The layout engine is what decides when what part and how HTML tags s 436 1152 master_ s zoomable s SVG files and visual elements are handled. For example IE has limited SVG support while Opera has the best support for interactive SVGs. The apparent differences in HTML5 support are also handled by this part of the browser. That is the reason this same HTML above shows up differently in older browsers like IE8. All the engines listed above are written in C++.n n 2. The JavaScript engine nEvery browser has a JavaScript engine which handles how the user interacts with the visual elements. For example the different JavaScript engines used by browsers are n V8 Chrome SpiderMonkey Firefox NitroSafari Carakan Opera Chakra IE9n The Java script engine processes how a user interacts with the page (everything happening in the background process). It executes all the JavaScript that tags along in the page.n A JavaScript engine affects speeds because n When the user interacts with the page (e.g. presses a button s some in the search bar etc.) the JavaScript engine processes the request and fills the search information back into the box. All AJAX calls jQuery DOM manipulation etc done in programs are also handled by this part of the browser.n The way the JavaScript is handled by each of these engines is different. Due to the javascriptpiler and handling of JSON data. Hence the difference in speed. For example Apple reserves the Nitro javascript engine for Safari alone and other developers are forced to use a different slower engine. This is the reason why Safari will always be the fastest browser in iOS. Some engines like V8 have some critical parts written in assembly and non critical parts in C++. All the other engines are written in C++n n 3. Cachingpression in the cloud nIn scenarios where band is limited the two factors listed above be less important. This is a game changer that makes the other two factors listed above kind of irrelevant (the code to be fetched is slower so they are in wait for the processing to start) up to a certain level. This technology was introduced by Opera - Opera Turbo.n Caching affects speeds because n The page is fetched by a serverpressed in terms of quality and so on to save data transfer. n 4. Local Caching nBrowsers also cache some of the content like scripts frequently accessed pages etc for later use. This leads to faster load times as the content is fetched from the disk instead of over an internet medium. This is the reason go is faster than reload by Kevin Ernest Long user 1427783 5. Plugin management nA typical user opens pages containing RIA (rich internet applications such as Flash Silverlight Java FX Quicktime etc) which handle video audio games etc in the browser. The way that these plugins are handled by the browser window and how it interacts with it are different. Chrome has built in Flash PDF support. The other browsers handle this differently. For example I am currently using Firefox. The process associated with firefox are Plugin management affects speeds because n Not to a large extent but the sluggishness that results when too many of these applications are opened is because of poor plugin management.n n 6. Memory management nEach tab is also to be given equal priority script execution and everything else mentioned above. The memory address of these has to be kept separate so that security breaches do not occur and one tab crashing does not case the browser to crash.n Firefox has 4+ tabs yet runs as a single process with as many threads. IE and Chrome open a separate process for each new tab. This affects the speed of tabs stability and the overall experience for the user.