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The list, available here, shows how much each add-on slows down Firefox at startup.
Ironically, an add-on called "FastestFox - Browse Faster" is on the list, together with several very popular ones such as the developer-oriented Firebug and bookmark synchronizer Xmarks.
The slowest add-ons on the list, FoxLingo - Translator/Dictionary and Firebug, slow down Firefox's startup by a whopping 74%.
The list is a result of a recent initiative by Mozilla to put a stop to performance-slowing add-ons. Mozilla announced it will perform automated performance tests of the top 100 add-ons hosted in its add-on gallery every week and display warnings for add-ons that slow Firefox's startup time by 25% or more.