I've found a few nice things for Mozilla Firebird, the IMHO least sucky browser right now (apart from being a memory hog).

The Permit Cookies extension does not do what its name implies, but gives you a popup for blocking/allowing/removing cookies for the current site on pressing Alt-c.

Why not allow cookies with all the other features enabled, especially "ask before accepting"? I had that, but I ran into major slowdown issues with a really big cookie permissions file which denied cookies for 99.8% of the sites anyway, and the question popup was very annoying, too.

So now I have cookies disabled in the global preferences as a good default, and for the few sites where I accept the requirement for cookies as sensible, I just enable cookies specifically for the site, once and comfortably.

Disabling cookies doesn't actually disable them: the explicit exceptions still work. The one thing I lose is the "cookies for this session only" functionality; that is taken care of by my mozilla wrapper which simply removes the cookie file on startup.

userContent.css in your profile dir/chrome/ is also quite useful for some things: the Firebird Doc Site mentions how to disable marquee tags, and here I found a tip on how to change the cursor for javascriptshite links:

a[href^="javascript:"] { cursor: crosshair; }

Flashblock is another saviour: flash crap is not displayed at all but a placeholder shows up. You can click on it and only then the flash thingie loads. Very nice, very useful.

The Tabextensionsextension is so common now that it has been properly Debianised - a welcome change from the lousy XPI installation mess mozilla tries to force on us otherwise.

Related to debianising mozilla and hand-installing extensions without messing everything up is this bit of info:

Mozilla on Debian gets its extension info from per-package files in /var/lib/mozilla-nameoftheday/chrome.d/. The good old run-parts-like approach works perfectly well here, too: you (or any package) can plop a file like 99azfixthisfuckingmess into said dir without affecting any other aspect of moz, and run update-mozilla-firebird-chrome to combine those files into what moz wants to see.

Looking at the XPI thingies (which are simply zipfiles) I usually find stupid javascript "installer" snort scripts which wouldn't do anything useful unless I run them as root (yeah, right, I'm as stupid as that). But it's not really hard to extrapolate from what you see in the install.js things, the bla.jar files (which are again simply zipfiles) and the examples set by mozilla-tabextensions to find a working install procedure.

So what I nowadays do to install extensions by hand but cleanly is rip the XPI apart and copy the bla.jar into /usr/lib/mozilla-nameoftheday/chrome/. Then I look at the install.js to see the register-something calls and populate my 99... fragment with the appropriate entries. Run the update program, restart moz, done.

Here's the entry dealing with the editcss extension as an example (they all look very similar):

content,install,url,jar:resource:/chrome/editcss.jar!/content/editcss/
locale,install,url,jar:resource:/chrome/editcss.jar!/locale/en-US/editcss/
skin,install,url,jar:resource:/chrome/editcss.jar!/skin/classic/editcss/