An essential part of lean code is lean browsing. Web browsers are often the most resource hungry program running on a personal computer, and a leaner web browser will mean less power used, less heat, less greenhouse gases produced, less crashes, and less need for CPU speed, RAM, and cooling.
There are a bunch of very lightweight browsers for Linux, such as Midori, Dillo, Hv3 and w3m. These prove that a browser can be well under 1 MB, be lightning fast to load, and still successfully browse. Unfortunately they are seriously lacking in features.
W3m is the most basic of these - it's a text browser (and there are others to choose from, if you're in the market). Text browsers are not something most users ever need to know about, but they do have niche uses. On to more practical choices (for most of us).
Midori, at about 350 kb, seems to do the best job of displaying pages the same way Firefox does - but it doesn't seem to save any cookies, and doesn't offer to remember passwords. You'll be logging in to your favorite sites every time you start Midori.
Nice idea, but not very usable, in my view. You can try them out if you're keen - if you run a mainstream Linux distro, they should be in your distro's repositories (except maybe Hv3).
There's a big jump here - the code for one these browsers is roughly 20 to 50 or more times the size of the flyweights.
Opera is an established, full-featured browser. It's claimed to be lighter than the mainstream browsers such as Firefox, and it might be, but to be honest I don't notice a huge difference - I can easily get it to 90 MB once I have a good number of tabs open.
It's not open source, and it doesn't quite manage everything as nicely as Firefox. I use this as a backup browser, e.g for checking secondary accounts without logging out of my main account.
Then there are browsers based on the same technology as Firefox, e.g. Kazehakase and Epiphany - again, they're likely to be in your Linux distro's repositories. But I wonder if the reason that these are faster is mainly that they don't have all the addons that we've installed on our Firefox?
I still find these to be a compromise - you're definitely giving up a fair bit in usability to have a lighter browsing experience - though Opera comes pretty close to Firefox in usability and fancy features.
If Midori would just save cookies, I'd say Midori was a much better trade-off than most or all of these.
SwiftFox and SwiftWeasel are two tweaked versions of Firefox, to improve speed and reduce memory usage. I haven't noticed a huge difference in speed, but there's a significant reduction in the RAM used by both of these, and that's A Good Thing. They're also very compatible with Firefox - I find I can install the same addons, and have had no problems with them at all. This is lighter browsing without compromising usability.
The main difference between these two projects is that SwiftFox is trademarked and the binaries are proprietary. If I've got it right, then in theory, the guy who packages SwiftFox might be doing something sinister. That's unlikely, but since I use this for my internet banking, I'm going with the security of a fully open source package, which means SwiftWeasel.
Unfortunately, they're only in Linux, and they're not in the repositories of most Linux distros. Installation can be confusing for a newbie, especially for SwiftWeasel (in brief: ignore the "source" packages, and install the latest "non-source" package, which is a compressed binary. Unpack into your home directory, and run the "swiftweasel" shell script. It needs an installation guide like the one for Flock.)
Firefox - the premier browser on all mainstream operating systems today. If you've got the resources, and/or don't share my bad habit of having way too many tabs open, this is a practical option. The only serious contenders for a better all-round browser, in my view, are those in the previous section, tweaked versions of Firefox.
Version 3 is a big improvement, and memory management was one of the areas they worked hard on. I still find it suffers from inflation of the amount of RAM used when it's been open a long time, but nowhere as badly as version 2 did.
But Mozilla people, please - could you please make it easier for us to tweak our installation of Firefox to make it less resource hungry? There are instructions out there, but relying on random blog posts and forums for instructions is dangerous. I broke my installation of Firefox that way, which is when I gave up on Firefox and tried SwiftFox, then SwiftWeasel. Really, I'd rather be able to keep using Firefox, and supporting the Mozilla Foundation for all your good work. So - could you please make it easier for us to be light and green in our browsing?
For now - SwiftWeasel is my recommendation for the average Linux user. But if you're a newbie or semi-newbie, make sure you've got support, from a Linux User Group or a geek friend - that might save you some hassles in installation.
Browsers for Windows
This is outside my experience (I used Firefox when I was last a Windows user, and it was all-round a better browser than Internet Explorer), but there seems to be talk on the web about lightweight browser for windows.