The move is part of a general overhaul of the add-on site, which will also feature more support for international users and new tools for user-to-user discussions.

But it's the thinning of the add-on herd that may raise eyebrows. "We're trying to tighten up the extensions, especially for new first-time users," said Mike Shaver, Mozilla's technology strategist.

Rather than list all the available Firefox and Thunderbird extensions -- Shaver estimated that there are approximately 2,000 available now -- the site will drop marginal add-ons, as well as those no longer maintained by their creator or not updated for the browsers and e-mail clients now in use. A couple of hundred extensions will remain on the site after Monday.

That list will change, said Shaver, because users will be able to nominate untried or niche extensions for promotion from what he called a "sandbox."

"Some extensions will be in the sandbox for a while, some will be moved to the public site," said Shaver. The idea is to make it easier for users, particularly new Firefox users, to find the most worthwhile and useful add-ons for the browser.