When it comes to the apparent single threadedness of both browsers, that is actually enforced by the execution model that JavaScript necessitates. JavaScript does not permit more than a single execution queue - scripts must be run to completion, in order, and must not be parallelised in such a way that it can be detected from script. That does not make single threading necessary, but it does make it hard to achieve any form of thread level parallelism. Note that we're just talking about the scripting model and not the UI or plugins. Everything that modifies structures that are script accessible such as the DOM, events etc. must be explicitly serialised from the point of view of the script. That is a bottleneck in using the entirety of CPU resources available.

However, networking, rendering, UI, plugin execution and so on are good places where parallelism can be achieved due to these being on either the input or the output side of the script environment. Or running multiple tabs in multiple threads, that might not help single sites to use the CPU to it's fullest, but it does allow several sites to not have to share the CPU resources with each other.

To really fix this, we'd need one of three things:
- New browser, plugin or DOM APIs that allow parallel execution while still preserving the apparent single threadedness of JavaScript's execution model, by moving all the parallelism into a black box from the perspective of the scripting engine.
- New ECMAScript constructs that allow for the code escaping the execution model using data immutability and message passing.
- New ECMAScript constructs that allow for transaction based programming on shared mutable data.

As it currently stands, there is very little JavaScript code out there that is programmed in a thread safe manner. (JavaScript lacks APIs and primitives to assist with this thread safety, as well...) It wouldn't be safe to even try to parallelise the execution of that code. Just imagine a menu script that on mouseover adds submenus to the DOM and on mouseout deletes them. What would happen if this script were implicitly parallelised by the browser so that more than a single event handler could run at any one time? An example of what could happen is that you're trying to add or delete nodes on subtrees that are in the process of being constructed or destroyed.

. I have analyzed your performance. You made a good conclusion your-selves. Yes, Firefox seems to be a winner, however your intend was to display efficient use of multiple tabs, idle time, and perceived performance and it shows that Opera doesn't stand behind.

Thanks for the comments, everyone. Unfortunately, it’s been my experience that most businesses have horror stories about SEO’s and web design companies.
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Well its quite simple i guess opera is out dated asn has some disadvantages over firefox so i always prefer firefox for my logo design work

Good to read all this keep sharing good stuff!
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As far as real performance Firefox seems to win in a few more test cases. However when Firefox wins, Opera doesn't lack much behind. In the case that Opera wins, the difference is bigger. When looking at perceived performance, switching tabs and scrolling, it's clear that Opera feels faster, more responsive. Especially scrolling can be proven by numbers, while opening multiple tabs also shows that Opera has more head room for handling user interface commands from the user. Unfortunately none of the browsers is able to use multi-core technology efficiently yet, as heavy JavaScript or Flash sites leads to 50% usage, which is the maximum of one core.

As far as real performance Firefox seems to win in a few more test cases. However when Firefox wins, Opera doesn't lack much behind. In the case that Opera wins, the difference is bigger. When looking at perceived performance, switching tabs and scrolling, it's clear that Opera feels faster, more responsive. Especially scrolling can be proven by numbers, while opening multiple tabs also shows that Opera has more head room for handling user interface commands from the user. Unfortunately none of the browsers is able to use multi-core technology efficiently yet, as heavy JavaScript or Flash sites leads to 50% usage, which is the maximum of one core.

Thanks for sharing. i really appreciate it that you shared with us such a informative post..
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I am looking forward for your next post, I will try to get the hang of it!
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Very Post.

Muito interessante. Parabéns!!

Good to read all this keep sharing good stuff!

That Opera has more head room for handling user interface commands from the user. Unfortunately none of the browsers is able to use multi-core technology efficiently yet, as heavy JavaScript or Flash sites leads to 50% usage, which is the maximum of one core. logo design

I think Firefox is maybe 100 steps ahead Opera and will be difficult to get passed by in the near future.

I didn't even know there was an opera...

Very well written article indeed, it really helps me with my programming skills, thank you so much for sharing such information with us, i hope we will see more from author in the future. Cheers.
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I think firefox is much better than opera because of its additional addons and features.
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It's obvious that each browser will return different results, but I think with more and more open source sofware and also "non-written" rules, all the browsers will evolve to one great browser!

Pretty good post. I just stumbled upon your blog and wanted to say that I have really enjoyed reading your blog posts. Any way I'll be subscribing to your feed and I hope you post again soon.
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Great article. COngratulations, gostei muito, parabens.

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I believe firefox must defeat opera!!!
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I am so impressed w/evernote so far. really pro stuff. thx folks

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