I’ve only done user-agent string sniffing once and I remember it gave me a headache… This post explains why it gave me a headache! 
And then Google built Chrome, and Chrome used Webkit, and it was like Safari, and wanted pages built for Safari, and so pretended to be Safari. And thus Chrome used WebKit, and pretended to be Safari, and WebKit pretended to be KHTML, and KHTML pretended to be Gecko, and all browsers pretended to be Mozilla, and Chrome called itself Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/525.13 (KHTML, like Gecko) Chrome/0.2.149.27 Safari/525.13, and the user agent string was a complete mess, and near useless, and everyone pretended to be everyone else, and confusion abounded.
via Daring Fireball
I’m a fan of the Tails plugin for Firefox… Now Safari (on Leopard) gets its own Microformats Plugin! 
Of course, in order to take advantage of Microformats and perhaps bring the information they offer onto your system, you need a browser that will read them - there’s Firefox plugins, and NetNewsWire 3.0’s built-in browser reads them. But what about Safari? Thanks to SIMBL, there’s a small array of Safari plugins available and from the maker of Safari Tidy comes Safari Microformats. Whenever visiting a site with Microformats, an icon appears in the right of the address bar (not unlike the RSS icon). Clicking it brings up a menu of available hCards and hCalendars you can add to Address Book and iCal.
via
Zotero is a new reference management tool that comes in the form of a Firefox (and Flock) extension. It looks like it could be a very good (and free) alternative to commercial reference management software tools like Endnote and Reference Manager. It even has plugins for Word and OpenOffice for cite-while-you-write functionality, and Wordpress so that writers of Wordpress based blogs can ensure that their posts are cleanly imported for users of Zotero.
Zotero [zoh-TAIR-oh] is a free, easy-to-use Firefox extension to help you collect, manage, and cite your research sources. It lives right where you do your work — in the web browser itself.
If you have any potential use for reference management (i.e. if you are a student or scientist) - I seriously recommend checking this out.
