Who says Firefox is only about Web browsing? Plenty of extensions exist for letting you share files, chat with one another, meet new people, and call them -- all without leaving Firefox. Yet without a single page for collaboration or social networking on Mozilla's extension site, finding those extensions isn't easy.

Enter Networking Pipeline's crack researcher (that is, yours truly). He braved the toughest of the Web, scoured extension sites, and crawled through the underbelly of the Internet to find for you the absolute coolest collaboration and communication Firefox extensions around.

The selection criteria were simple. First, the software had to be a downloadable, publicly available Firefox extension. Second, the software had to be collaborative in nature. This means just what you'd expect: It had to allow two or more people to work together.

We uncovered 15 extensions that fall into five functional groups. Telephony clients let users call, and often IM, one another. Social searching and bookmarking extensions use social recommendations to help searchers locate Web sites of interest. Co-browsing coextensions turn Firefox into a tandem browser, and chat extensions let users text-message other users on a Web site.

Have we hit every collaboration extension for Firefox? Probably not -- the Web is a pretty big place, after all. So please e-mail me for inclusion in our next top Firefox collaboration extension list. Telephony Clients
For Skype lovers, calling within Firefox combines the best of both worlds -- free phone calling and the convenience of not having to jump out of your browser to place the call. Well, almost. Phone calling is only free on-net, of course, and most VoIP extensions are really just standalone clients launched from a button bar in Firefox.

The new Abbeyphone extension is the exception. Released on June 6 by an Italian company, Abbeynet, for use with its Abbeyphone SIP service, the extension runs as a dialer on the bottom of Firefox bar and allows users to call, hang up, and see the amount of credits on their phone service without leaving their browser. Users can also send SMS and dial a phone number on Web page by highlighting and selecting an option from the right-click menu, writes Luca Filigheddu, Abbeynet's CEO of ICT operations, in his blog.

The Abbeyphone extension, though, doesn't offer free PC-to-PC calling, nor does it provide for IM and video. For those capabilities you'll need to go to multifunction clients -- i.e., the Skype competitors, such as OpenWengo and Zoep. OpenWengo runs in the Firefox sidebar, Zoep in an external window. Both provide IM and voice. OpenWengo is the more mature of the two. Unlike Zoep, the company claims to offer video, allow users to change their presence status and send emoticons, and offer some of popular functions available in the Gizmo client, such as being able to see the physical location of an individual on a map. Social Searching
Finding highly valued Web sites is largely what Internet research is all about, but searching through the millions of sites returned by Google or Yahoo is hardly practical. Social searching and social bookmarking are two different attempts at addressing that problem. By gleaning user preferences, they can improve the quality of the links delivered back to the user, either as search results, site lists, or cues on a Web page

While Yahoo's MyWeb, Google, Wink, and Prefound have made waves in social search, few extensions make the technology available for Firefox. There is Search Party, but it's only compatible with Firefox 1.0 to 1.4.

Outfoxed is an exception. Stanley James built this alpha release, based on his master's thesis at the University of Osnabruck, Germany, that uses your social networking information to determine the good and the deadly on the Internet. The idea behind Outfoxed is that people make decisions based on a close circle of experts whom they trust. By sharing bookmarks, chains of trusts can be established, giving users an ever-expanding circle of "experts" to advise them on the Web. Social Bookmarking
As for social bookmarking, you probably know about the Del.icio.us and the Firefox extension for Del.icio.us. You might have heard about IBM's enterprise social bookmarking project, Dogear, but are you familiar with Yoono? Yoono is a Firefox extension that combines social searching and bookmarking. Yoono first synchronizes your bookmarks with those of others on the Web and then uses a site's popularity as an evaluation of the bookmarked sites. When viewing a site, clicking on "See Suggestions" takes users to a page considered to be of higher interest, based on the popularity of the site within bookmarks. (A rather long list of social bookmarking sites can be found on listible.)

Co-Browsing
Too often, the Web experience is touch-and-go when you try to view a Web page at the same time as someone at a remote location. They can waste time looking for a page or element, only to end up at the wrong site. It would be so much easier if you could stretch your arm through the computer screen into their office and point to the particular site or element.

Well, now you can. With a co-browsing extension such as Jybe, users can browse the Web together. Users create "sessions" and invite others to join them. Sessions may be open to everyone or closed, protected by a password. During a session, Jybe opens a chat bar on the bottom of the screen so users can text message as they browse. A side panel lists the names of the individuals involved in the session.

While co-browsing works well for surfing the Web together, businesses will also find that co-browsing has other practical applications. Presentations, for example, can be loaded into a browser window and viewed by all, much a like an inexpensive WebEx solution. Chat For Web Sites
Chat is by far the most popular type of collaboration extension for Firefox and the easiest to find (in small part thanks to the list of applications on Virtual Presence.org). These add-ons turn any Web site into a chat forum, for better or worse.

On the one hand, these applications allow for extemporaneous social interactions between people. Surfers can meet one another. E-tailers get to sell their site visitors. On the other hand, these extensions are in their infancy, often hampered by clumsy interfaces, questionable security, and nominal popularity.

The most unusual of the chat systems is Lluna from Bluehands, a German social networking company, with funding from SurfNet, the Dutch academic network. Though not a Firefox extension, Lluna uses a Firefox extension, Llunahelper, to shuttle URLs to an external application.

At first, I had a difficult time getting Llunahelper to run under Firefox. After much research, Bluehands' designer, Heiner Wolf, was able to reproduce the problem. The problem, he wrote in an e-mail, was that another one of my extensions, StumbleUpon (see below), somehow damages the browser's data structures where Llunahelper extracts the current URL from Firefox. "Since StumbleUpon also works with the current URL, I bet that they accidentally overwrite something," he wrote. The Llunahelper version 1.2 should correct the problem . "If not, then the general Firefox cache must be cleared."

Lluna presents avatars for the users viewing a site on the bottom of the Web page. Users can IM and chat with another, walk over to one another, use white-boarding tools to mark up a Web site, and co-browse the Web. Future releases will use VoIP so users can speak with one another. When that happens, Lluna users will likely be able to telephone with a large, pre-existing user base. The product is based on the XMPP protocol, the same protocol underlying GoogleTalk and Jabber. SamePlace is a chat extension also based on Jabber that uses a chat window in the sidebar instead of avatars on a page.

2006 Netmite Communities 2.2 adds a Firefox sidebar that allows users to post and review comments about a Web page. Users can also participate in group or individual discussions tied to or separate from a Web page and rank other user's postings. Personally, I found Netmite's interface to be clunky, but there's probably no other chat client that competes with its functionality or traffic volume.

Ajax is starting to be put to good use by some extension developers. Gabbly is an Ajax-based chat extension that runs as a Firefox sidebar. It's unique in that it delivers transcripts of the chat session by RSS. Chatsum is also a slick-looking AJAX-based client that provides an easy way to find other chatters.

With the Yakalike extension, users navigate channels associated with each Web site in a frame at the bottom of their browser. Channels can be found by clicking on the "popular-channel" button or by simply viewing the site where a small window lists the users on the site.

For those IRC diehards, the Peeko Chat extension adds an IRC text bar at the bottom of the Firefox window. Site viewers can see who else is on the same Web page and then chat with one another through text commands. Alternatively, they can launch ChatZilla, a Firefox extension that runs as an external client for chatting on the IRC service.