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 donít realize add-ons can cause these delays, and thatís why weíre 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 thatís 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 Firefoxís start-up time.