- Mozilla has released a list of 10 Firefox add-ons that affects the browser’s performance the most. The list have been compiled by performing automated tests on different add-ons by Mozilla. If you have any of the listed plugins installed, we recommend you to remove them immediately for faster browsing experience.Press Release:Slow Performing Add-onsAdd-ons provide many useful features and functions, but they can also cause Firefox to become slower. Some add-ons can even slow Firefox to a crawl and make it difficult to use for regular web browsing. If you think add-ons might be the reason Firefox is lethargic, check the list below for some of the biggest bottlenecks. And remember, for best performance you should disable add-ons that you no longer use regularly.