Today seems to be Firefox/Iceweasel 3 Bashing Day on Planet Debian, so let me join the fun :)
I agree with most other people that the default Firefox/Iceweasel 3 config is not ideal, so here's what I did to fix it. Some of these items improve performance, some remove annoyances, some remove privacy issues, some remove security issues. Not everything here may be desirable for people other than me.
Select "Edit / Preferences".
Open a new tab, enter "about:config" as URL and hit ENTER. Click the annoying "I'll be careful, I promise!" button. Uncheck "Show this warning next time" while we're at it.
browser.urlbar.matchOnlyTyped = trueto disable the new, annoying "AwesomeBar" URL bar feature (which is also a huge privacy risk).
browser.tabs.tabMinWidth = 60and
browser.tabs.tabMaxWidth = 60(needs a browser restart). You can even use less than
60if you don't need any text and an icon per tab is enough for you.
extentions.getAddons.showPane = false.
bidi.support = 0. You'll probably never need it, so reduce the number of potential bugs and security issues by disabling it.
browser.ssl_override_behavior = 2and
browser.xul.error_pages.expert_bad_cert = true(thanks Pierre Habouzit).
browser.tabs.closeButtons = 3in order to prevent accidental closing of tabs (no more Close buttons on each tab, only one global Close button on the right). Yes,
CTRL+Shift+Thelps in case it still happens.
network.prefetch-next = falseto prevent random prefetching of webpages which means wasting CPU cycles and bandwidth, as well as subtle privacy and security issues.
None. Don't even think about installing crap like the closed-source Flash player if stability or security are important to you. If you absolutely must watch YouTube videos, I recommend youtube-dl.
Use as few as possible. Every extention may have security problems or bugs, and can negatively affect performance etc.
I've been a happy Privoxy user for quite some time now. I can really recommend it to anybody who wants to get rid of all the nasty stuff floating around on the web these days. From the Privoxy homepage:
Privoxy is a web proxy with advanced filtering capabilities for protecting privacy, modifying web page content, managing cookies, controlling access, and removing ads, banners, pop-ups and other obnoxious Internet junk.
The most useful feature for me is that it automatically removes almost all of those ugly flash-based ad banners.
My todo list: