Moziilla is outing add-ons that degrade the start-up speed of the latest version of Firefox

Topping the list is Lunkular's FoxLingo translator, which Mozilla says slows down browsers by 74 percent. The add-on supports over 3,000 languages and has been downloaded over 4 million times. Tied for first place is Firebug, which has been downloaded over 34 million times despite its 74 percent slowdown.

One notable entry in the list is FastestFox-Browse Faster, an add-on billed as a way for users to increase their productivity. Regardless of its claims, FastestFox-Browse Faster slows Firefox down by 33 percent, Mozilla says. 

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, Mozilla Product Manager for Add-ons Justin Scott wrote. 

Scott said that Mozilla would soon be doing weekly automated performance tests on the top Firefox add-ons, and issue performance warnings for the most severe abusers

Mozilla recommends users disable add-ons they do not use on a regular basis, estimating that, by installing ten add-ons users could double the time it takes for their browsers to load. 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, Scott wrote.