File Under: Browsers

Slow Firefox? Mozilla Says Add-Ons Are to Blame

Does Firefox feel like snail on the tubes? Blame the add-ons.

If the new Firefox 4 isn’t fast enough for you, Mozilla says add-ons are likely to blame. The ability to extend Firefox with add-ons is a large part of the browser’s success, but those add-ons come with a cost.

According to Mozilla, “installing 10 add-ons will double Firefox’s start-up time.” In some cases poorly written add-ons can slow down the browser even more.

The slower start-up times make Firefox look bad, even if add-ons are responsible, which is why Mozilla is launching a new effort to improve Firefox add-ons.

Mozilla’s automated testing highlights the worst offenders, which include widely used favorites like Firebug (#2) and AdBlock Plus (#12). Firebug slows down Firefox startup times by 74 percent, while running AdBlock Plus will slow down start up time by 21 percent. In the latter case, AdBlock Plus developer Wladimir Palant, says the problem is simply the size of the ad-blocking lists.

“Even with all the caching done in the current Adblock Plus version,” writes Palant, “loading up EasyList with its 11,000 filters is taking its time.”

To combat the problems with add-ons, Mozilla has announced it will begin labeling add-ons that slow down Firefox. The Mozilla Add-ons site will soon begin displaying warnings on any add-on that slows Firefox start-up time by 25 percent or more. Future releases of Firefox will go even further, adding the warnings to the Add-on Manager as well.

Though which release isn’t specified, Mozilla says an upcoming version of Firefox will stop third-party add-ons from being installed until users explicitly opt in. That means third-party software running elsewhere on your computer won’t be able to install toolbars and other bundled add-ons without your permission.

The warnings about slow add-ons will hopefully help Firefox users make more informed decisions when it comes to weighing down Firefox with dozens of add-ons, but if those add-ons are an irreplaceable part of your browser experience, simply turning them off isn’t a realistic option.

To help speed up what many consider the best part of Firefox, Mozilla is reaching out to developers of slow add-ons and asking them to work on performance. The company has updated its Performance Best Practices for add-on developers and is encouraging developers to optimize their code. Mozilla also plans to release developer tools designed to help add-on creators speed up their work.

Another option for some add-on developers will be the coming JetPack extension system, which is currently in its fourth beta release. JetPack is a new extensions framework for Firefox designed to offer developers an easier, faster way to build browser add-ons using common web-development tools like HTML, CSS and JavaScript.

JetPack add-ons are very similar to the add-ons you’ll find in other browsers. Due to the limitations of JetPack, not every add-on will be able to switch to the new framework, but those that will won’t have nearly the impact on browser performance that traditional add-ons can incur.

Snail photo by Dan Machold/Flickr/CC

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