Firefox, Ubuntu's default Web Browser, is a highly extensible piece of software. It's basic functionality can be enhanced in myriad ways through the use of Open Source, often community maintained extensions. Here I'm going to summarise a few extensions that I find very useful. The first two enhance security and so come highly recommended for all users. The rest however are merely enhancements that I find useful (and hopefully you will too) but are by no means necessary.
Web Of Trust (WOT)
Web Of Trust is another highly-useful security enhancing add-on. It will warn you if the site you're trying to visit is likely to attempt to deliver malware, send spam, scam visitors or is not child-friendly. While malware is generally not a problem on Linux, scams and spam are of course platform agnostic so this add-on is still highly useful and highly recommended. It uses a simple traffic light system (green for good, yellow for caution and red for don't bother!) and will even unobtrusively integrate with most popular search engine results.
BugMeNot is a great little extension that will allow you to bypass compulsory web registration forms. You know the type of forms I mean – those arbitrary registrations you have to make just to read a newspaper article on the newspaper's website. That sort of stuff. It will not allow you to log in to a pay site, or anything that requires registration for security purposes - such as social networking sites and forums etc.
Does just what it says on the tin! Simply highlight any word or phrase, right-click and choose Lookup in Wikipedia from the context menu. Et voilà!
This extension simply integrates that mildly annoying floating download window that FF uses into the main window. Simple. Elegant. Useful. What more could you want?
This one is more aesthetic than anything else. It just integrates the progress bar for page loading into FF's address bar. It can be customised to use any colour or even background images. Useful as a quick visual reference.
A useful extension allowing you to grab embedded Flash video from most websites that use it – such as YouTube etc. It does this via a little animated icon on the left hand side of your address bar. When you watch a Flash video online the icon starts to spin slowly, indicating the video stream can be downloaded. Simply click the icon, select the video and a download location and away you go. It also comes with a large list of sites that it supports.
User Agent Switcher
This comes in handy for those rare sites that aren't standards compliant and won't work properly with anything but Internet Explorer or the like. It simply makes Firefox report itself as Internet Explorer, Netscape or Opera. It can be found under the Tools menu. Always worth a try if the site you're browsing won't work properly in Firefox.
FEBE (Firefox Environment Backup Extension)
Last but by no means least is FEBE. This helpful extension allows you to quickly and easily backup you Firefox profile to a location of your choosing. This includes all your extensions, bookmarks and preferences. Very useful for those times you need to re-install FF for whatever reason. It will also restore your profile from a saved location too. Great stuff!
These are just a few of the thousands of add-ons available for Firefox. Go to the Firefox Customisation Page and have a look for yourself. Chances are, if you're looking for specific functionality, someone has already created an extension to do it. Happy hunting! :)