Here's a couple of pages you can use to examine your HTTP requests; one which displays your HTTP request as a CGI script sees it (no-cache version), one which just echos your request back at you (no-cache version) (with some caveats), and one which processes your request and shows you the results in tabular form.

Inspect This (Mozilla extension)

"Inspect This" adds an entry to your browser context menu, allowing you to open up the DOM Inspector for whatever element you right-clicked on.  Install It!  (I'm no Mozilla/XUL/Chrome expert, so I based this on "Nuke Anything" by Ted Mielczarek). 

Update, April 2006: recently an extension offering the same functionality has been added to addons.mozilla.org.  You should probably use it in preference to my version.

Find unused rpm / dpkg packages

These two scripts (one for "rpm" packages, e.g. Red Hat; one for "dpkg" packages, e.g. Debian) find out which of your currently installed packages aren't needed (based on a list you feed it, of the packages you do need).  Each script simply produces a list of unused packages, which you can then feed into rpm --erase or dpkg --remove, for example (i.e. neither script actually does the "remove" for you). 


Download: find-unused-dpkg; find-unused-rpms

Installation: unpack the archive. Copy the script to /usr/local/bin. Copy the example config file to /etc, removing the ".default" or ".example" suffix.


See the list of greasemonkey scripts.