Firefox Essentials
I haven't always used Firefox. Before there was Firefox, there was the Mozilla Suite; and after the Mozilla Suite fell, there was SeaMonkey.
I used SeaMonkey for a while, after the Mozilla Suite was discontinued. I switched to Firefox somewhere around version 2. Firefox 1 was simply unusable. What changed from 1 to 2 is that most of the the extensions i relied on in SeaMonkey got ported to Firefox, and extensions were written to bring back features which Firefox had shed. This was not surprising, given how much better Firefox's extension support was. ("What!? You can uninstall extensions? And you don't have to reinstall them every time you upgrade?")
So now i use Firefox. And, at this point, there is nothing else i can use. I rely on too many extensions to switch to anything else. Here they are:
AdBlock Plus The web is so much nicer without ads. Here is a round-up of posts about the ethics of ad blocking: The Devastating Effects of Ad Blocking. Tree Style Tab
I have a lot of tabs open. Care to guess how many? 20? Too low. 50? Keep going. 100? I wish; give up? 200? Getting closer. Here, i'll tell you: my current count is 368.
With more than a couple dozen tabs, the tab bar quickly becomes useless. Tree Style Tab puts the tab bar down the side of the browser, and also arranges them in a heirarchy.
This is by the author of Tabbrowser Extensions for the Mozilla Suite, which i used for a while until i realized it broke too many things. Later i discovered Multizilla. When Firefox 4 comes out, i'll probably jump ship to Vertical tabs.
BarTab Here is a marvelous invention: an extension which frees the memory of tabs which you aren't using. This is how i can have over 300 tabs open on my pathetic computer. My only quibble is that it doesn't interact perfectly with Session Manager. Fix for bug #469082 Bug #469082 makes me mad every time i read it. This extension brings back browser.link.open_external, except i rewrote it to use the eval() hack so as to work with Tree Style Tab. You may want to use Tabs Open Relative (Modified) instead. Tab Counter Lets me keep track of how many zillions of tabs i have open. Sometimes i wish it could show how many tabs BarTab actually has loaded. NoScript A JavaScript whitelist. Not only more secure, but possibly improves performance. CookieSafe Lite CookieSafe is like NoScript for cookies. Before i had CookieSafe i would set the cookie policy to "Ask me every time". This got super annoying. No more! Now i block all cookies by default; and if a site needs to set cookies, i reach down to the status bar and click "Allow example.org". CookieSafe also has a "Last 10 hosts" window, in case you're on one of those sites that uses 5 layers of redirection on its login page. Session Manager Session Manager builds on Firefox's built-in SessionStore API to provide a replacement for SessionSaver. Firebug Absolutely essential when you're trying to figure out why your CSS isn't working. The JavaScript debugger is nice too. NoSquint Site-specific zoom levels. Also allows you to change the default zoom mode back to text-only. Ctrl-Tab Makes Ctrl-Tab in Firefox behave like Alt-Tab in most window managers. That is, it moves in most-recently-used order. Lazarus Never again lose that 5000-word forum post you were working on. Greasemonkey My main use for Greasemonkey is to replace embedded YouTube videos with a link to the video. Stylish Like Greasemonkey but for CSS. I only use this to correct some egregious fixed-width layouts. Link Widgets Toolbar buttons which provide access to and friends. JSONView Like Firefox's built-in XML viewer, but for JSON. Web Developer toolbar Miscellaneous useful tools. The two i use most often are "Disable cache" and "Show passwords". Download Statusbar Menu Editor MR Tech Toolkit Readability SkipScreen Tabberwocky