How-To Geek

Ever Wonder Which Firefox Add-ons Slow You Down the Most?

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The best thing about Firefox is that it’s incredibly customizable, but have you ever wondered how much of a price all those add-ons take? Here’s how to see which add-ons slow down Firefox startup time the most.

Thanks to @codinghorror for pointing it out on Twitter, we can now know for sure, thanks to Mozilla Add-ons list of slow-performing extensions during startup—this doesn’t mean they necessarily slow Firefox down once it’s loaded, of course.

The fun part is that #8 on the list is the FastestFox extension, which is supposed to make Firefox faster. Instead, it seems to slow down the startup by 33%, though it’s not the only popular extension to make the browser slower—Xmarks, Adblock, NoScript, and Greasemonkey all slow the startup down as well. If you’ve combined them all together, you’re looking at much slower startup speeds.


Head over to the list, and see if your favorite add-on is slowing Firefox startup down for you.

Firefox Add-ons with the Slowest Start-up

Lowell Heddings, better known online as the How-To Geek, spends all his free time bringing you fresh geekery on a daily basis. You can follow him on if you'd like.

  • Published 04/6/11

Comments (20)

  1. Santo

    This is the list that I was waiting for.

  2. dave

    How ironic, something called FastestFox- Browse Faster, makes your browser 33% slower. Welcome to the internet new home of the SnakeOil salesman.

  3. Deed

    For Adblock Plus, I’ll take the 21% speed hit.

    Foxclocks is worrying – it doesn’t even do much and yet creates a 46% speed decrease?!

  4. Mathyabus

    I agree with Deed the 21% from Adblock Plus is worth it. I’m also glad to see its the only addon i use in this list

  5. Alex Thorp

    This really doesn’t bother me. I restart firefox every time the memory usage jumps above 1GB. At that point it is already slow because it has to restore so many tabs, and instances. For the better browsing experience I get from these add ons; it is definitely worth it.

  6. Carlos Ferrari

    @dave : exactly what I was about to say.
    Worse than that, I use it and I like it but I have to say it’s one of those addons for lazies which means it’s completely avoidable.

  7. Mike

    Adblock and NoScript stay no matter how much they slow it down! Very much worth the tradeoff!

  8. sue

    For Cool Previews and Ad Lock plus – who cares – could’nt live without either of them

  9. Lucky

    Great list! I’ve been looking for something like this. With the right add ons FF4 might just replace IE9 as my default browser.

  10. Butler

    I use fastest-fox. It adds maybe a half second to the browser startup time, and then has no noticeable effect on browsing speed.

  11. Shadow

    It would be interesting to do the same thing for chrome :)

  12. dave

    Anybody else suddenly get email from “Jeanet ” after posting here? The troll even admitted getting my email address from here.

  13. Woot

    @Deed, I’m totally with ya on that, mate!

  14. Liz

    thanks for that, however I never load anything new, I always wait for those eager beavers to work out the problems, but I did notice that my download manager stopped working and I had to and reset it all over again. Anybody else had the same problem.

  15. HellScream

    hhhmmmm so flashgot is the reason why my FF is kinda slow…

  16. rich

    So… other than load, can we assume an installed, _idle_ addons does NOT degrade performance?

  17. cam2644

    I’ll put up with Adblock Plus and Video Download Helper slowing me down a fraction

  18. John Ortiz

    Feedly is not in the list! OK!

  19. Lassar

    Firefox was really slow ,till I disabled flashgot.

  20. Mika

    I noticed that even with Adblock I still get pop ups and shit.. I mean is it really worth it to have it if you have a crap computer that slows down easily?

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