Find Out Which Add-Ons Are Slowing Down Firefox

Find Out Which Add-Ons Are Slowing Down Firefox

We’ve always known that installing a lot of add-ons can slow down your browser, but Mozilla’s now telling us just how much. Here’s a look at, generally, how much an add-on will slow you down, and some of the worst offenders.Mozilla says that, on average, each add on adds about 10 per cent to Firefox’s startup time:

On average, each add-on you install adds about 10% to Firefox start-up time. For some users that’s mere milliseconds, and for others it may be half a second; it all depends on the hardware and software of each individual. Many add-ons add less than 10%, and unfortunately, there are quite a few add-ons that add more. But based on our real-world performance data, installing 10 add-ons will double Firefox’s start-up time.

That’s pretty useful information. However, Mozilla’s taking it a step further and showing you which add-ons are the worst. Mozilla is now performing automated performance tests of the top 100 add-ons in its gallery, and displaying the results on this page. If you see one of your add-ons on that list, you know it’s seriously affecting Firefox’s speed. It’s definitely worth a look — at the time of this writing, the list contains some pretty popular add-ons, like FoxyTunes, Xmarks and (ironically) FastestFox. Of course, this will change as developers start to improve their add-ons after being shamed by their presence on this list. Right now you can view the top 50 offenders.

Starting in the next two weeks, Mozilla will also be adding “slow performance” warnings to these add-ons when you install them, so you won’t have to keep checking the list every time you install something new. They’ll also be reaching out to developers and helping them improve their add-ons, which is pretty great. For now, head over to the list to see which add-ons might be slowing your system down, or check out Mozilla’s blog post for more information.

Slow Performing Add-Ons [Mozilla via Mozilla Add-Ons Bog]


  • Startup time doesn’t seem like a useful metric to me. I don’t know about others but I keep Firefox open for days, even weeks. I’m more interested is which plugins are causing the constant 10% CPU use that I see

      • I agree it is an irrelevant figure to a lot of people, but it is still worth having.

        Though if you have an SSD all programs will start up instantaneously anyway.

    • @Boyd – Yeah I’m with you – My computer is on 24/7 and firefox is open days at a time.

      More important is keeping the resources and CPU cycles low although Firefox is much better at this now than it used to be.

      In the old days 10 tabs sent it into a spin – Now I can have 30-40 tabs open without too much fuss (yes I know – but i like to keep opening new tabs when I’m researching)

  • So,.. They aren’t causing it to run slow,.. just start up slow,.. I don’t care about start-up I care about whats causing web pages to lock up or load incredibly slowly,… :[

Log in to comment on this story!