Extending the browser
I rarely use Internet Explorer as my web browser; I mainly use Firefox 3.5 because of Firefox's superior and extensive range of "Add-ons" (http://addons.mozilla.org/). These add-ons, or extensions, extend Firefox's abilities and you only need to install the ones you need. Here are a few I regularly use...
Research Do you regularly do research on the internet, especially in relation to useful parts of cases and legislation from sites such as AustLII (http://www.austlii.edu.au) or the NSW legislation site (http://www.legislation.nsw.gov.au/)? I regularly copy and paste information into a new document and track the url where I found it. Microsoft OneNote is good at that, but requires Internet Explorer, so I've tried a few other ways and have settled on iCyte (http://www.icyte.com). It's a Firefox add-on that lets you select and clip parts of web pages, saving the selection, url, tags and notes in one step into logical collections. I very quickly found it enormously time-saving, and a great way to do any kind of internet research. It even works on large Intranets.
Passwords I go to hundreds of web sites that require a login of some sort. I have a couple of low security passwords that I regularly use, but I require a number of complex one-time passwords for several important sites. I just can't remember those passwords, much less which one I used at a given site. Roboform (http://www.roboform.com) and lastpass (https://lastpass.com/) are both excellent password managers, but I'm a longtime Roboform user and prefer it. Lastpass is free and almost as good.
Favourites Bookmarks or favourites are great to have, but by default they only exist on one computer. If you go home or change computers you don't have access to your other bookmarks. There are many solutions to this problem, but I prefer Delicious (http://delicious.com/) which is owned by Yahoo! You can store and categorise and even share your bookmarks, and the Firefox plug-in is quite powerful. You can also access your bookmarks if you are using someone else's computer or at an internet cafe.
Switching While Firefox is a better web browser than Internet Explorer, there are times when you need IE. The add-on IE Tab solves this by allowing you to stay in Firefox but use the IE rendering engine either on a custom basis or permanently for selected sites.
Task management Outlook's task management is pretty crude, and I've found that RTM (http://rememberthemilk.com) provides far greater ease of use, it's not bound to one computer or system, and plugs into GMail and iGoogle. Creating a new task by typing "Tomorrow at 9:30 ring James" or "Get haircut every three weeks" is pretty intuitive, and repeating tasks can be made to reset when the previous task is actually done, not when it was scheduled to be done (useful for haircuts).
Speeding up the browser While advertisements help fund a lot of internet sites they are often obtrusive and particularly slow to load, which makes the whole page slower. Adblock Plus comes with a preconfigured list of sites that supply advertising copy, and it prevents data and images from those sites loading. You'll be amazed how much it cleans up a page and speeds things up. However, sometimes you will miss content because some suppliers provide both content and advertising from the same system.
Snapshots of web pages If you practice in intellectual property you may need to grab screen shots of web pages at points in time. One way is to use Adobe Acrobat, but FireShot is free and flexible.