Firefox

Tabbed browsing is one of the features that makes firefox really shine. You can go to File -> New Tab, or just hit CTRL+T and you will have a new tab open up.

Recommended Plugins
NoScript prevents unwanted java/script or flash from running in your browser. In 2008, most of the computers that were broken into was because they were not running this. When you install NoScript, you probably about to go to about:config and change

noscript.firstRunRedirection

from true to false. This will stop it from going to NoScript's ugly website after each upgrade.

Torbutton allows you to surf the web anonymously, however it also requires you have tor installed.

Permit Cookies is used to set cookie permissions for the site you are viewing.

Ad blocking
Sick of seeing advertisements on webpages? It's very easy to combat this with the adblock plugin. If you attempt to download/install it and it fails, with a beige bar appearing across the top of your browser, and a tab on the far right of that bar that reads "Edit options", choose "Allow" and then "Okay" and then you should be able to install it okay.

If you don't want to wait while you build your own adblock rules, do a search for "adblock rules" online and download that list to your desktop. Once you've restarted firefox, hit SHIFT+CTRL+P (or go to Tools -> Adblock -> Preferences) and select "Adblock options" where you will see an option to "import filters". Use this on the adblock.txt you found from your "adblock rules" search and you should be set now. Go to your favourite ad loving website and see if you can see any banners.

Anytime you see a banner on a website now, you can simply right click on the banner and choose to adblock the image. You can also use wildcards in adblock rules which is very handy as you may have noticed in your adblock rules.

*adserver*

is one of my rules for example, which blocks any file with the word adserver in the URL. If you have it installed and have restarted firefox, you should now search online for "adblock rules" and download a comprehensive set.

CTRL+SHIFT+P opens adblock preferences. "Adblock Options" -> "Import filter" and then choose the adblock rules file you just downloaded to your desktop. You should no longer see any ads, anywhere. If you do, you should be able to right click on them and block them so you'll never see that one again.

There is also adblock plus

Remove lockfile
If you're forced to kill firefox, or it crashes, it will often leave a "hidden" lock file around. You will know this has happened when you open firefox and a window opens up asking if you want to to use "Default profile" or not.

find ~/.moz* -depth -name lock

This should find the lock file for you. If it has, then you can add | xargs rm to the end to remove it.

find ~/.moz* -depth -name lock | xargs rm

or if you don't want to run two commands: find ./.moz* -name lock -exec rm {} \; and now you can open firefox as per normal now.

Hacking
If you want to really play around, type "about:config" in the URL bar of your Browser. You can make some really useful modifications, but you can also make things worse so be careful making any changes. Restart firefox when you've finished your changes.

Try entering any of these URLs into firefox to see what happens.

chrome://global/content/alerts/alert.xul

is one of the more entertaining. CTRL+W to stop it.

Ramdisk
[| Create a Ramdisk]

Disabling DNS prefetching
DNS prefetching reveals a great deal about the contents that you're browsing to the DNS server. I personally don't like it and found it to be enabled on OpenBSD's default firefox. Type about:config in your browser navigation bar and filter for this string: network.dns.disablePrefetch you then right click to "New" and create a boolean value with that name.

More food for thought. If you're using offline intranets the prefetching will reveal to the DNS server what sites are linked from the pages you visit. DNS is probably the least filtered protocol out there so it may reach all the way to the root nameservers, who gobble up your info.