Firefox performance is extremely important to our users, especially how quickly it starts up and loads websites. Customization is also extremely important, and while most add-ons cause only a tiny performance impact, others can significantly slow down Firefox. Many users don’t realize add-ons can cause these delays, and that’s why we’re committed to improving performance in a big way.
How slow are we talking about?
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.
What is Mozilla doing about it?
We’re excited to announce a number of initiatives we’re working on to reduce the performance impact of add-ons through developer tools, documention, and user education.
- Automated performance testing — Every week, we perform automated performance tests of the top 100 add-ons hosted in our gallery and display the results. Soon, we will automatically scan new versions of all add-ons as they are submitted. In the coming months, we will expand this to include other measures, such as page load time.
- Slow performance warnings — In the next two weeks, we’ll begin displaying warnings in our gallery for any add-on that slows Firefox start-up time by 25% or more. We think users deserve to know when an add-on will impact them and want them to make an informed decision to install the add-on. In an upcoming version of Firefox, these warnings will be displayed in the Add-ons Manager as well.
- Performance documentation and outreach — We’ve updated our Performance Best Practices and have begun reaching out to developers of slow add-ons and asking them to work on performance. This isn’t limited to add-ons hosted in our gallery; it includes all slow add-ons we can find.
- On-demand performance testing — In the coming months, we’ll provide tools for developers to upload an add-on and receive a performance report to test the effectiveness of their fixes on the same machines that officially rate their performance.
- Required opt-in for installation — It’s an all-too-common practice of third-party software to install toolbars and other bundled add-ons in your browser without permission. We know that these add-ons account for many of the performance problems reported to us, and users often don’t know how the add-on got there or how to remove it. In an upcoming version of Firefox, third party add-ons will not be installed unless the user explicitly allows the installation in Firefox. We expect this to have a huge impact on Firefox performance, as well as giving users back the control they should have over their add-ons.
What should add-on developers do?
- Test in all the possible configurations a user might encounter.
- Learn the Performance Best Practices and use them when developing your add-ons.
- Optimize your add-ons, aiming for 5% start-up impact or less.
If you need help or have questions, ask us. We’ll soon be providing additional documentation, tools, and advice on improving performance.
What can Firefox users do?
The best way to combat slow add-ons is to disable add-ons you no longer use. Disabling an add-on will prevent it from loading and slowing down Firefox, yet keeps it in your Add-ons Manager so that you can re-enable it anytime you’d like.
Firefox users shouldn’t have to choose between customization and performance, and with the help of add-on developers and the Mozilla community, they can have both.
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