Progress? Firefox Debug Builds on Ubuntu 8.10

I expected to have released a new version, but on finally using the Bittorrent extension on torrents with data greater than 300Mb, I can see that the memory usage is quite horrid, and memory isn't released when downloading is finished.
So now I'm stuck in trying to debug to find why memory isn't released, which brings me to getting a debug build on Ubuntu 8.10.

Building on Ubuntu 8.10

DO NOT follow this guide. You'll be building an OLD Firefox. Check out jboston's user page; you MUST use Mercurial (hg) to get the latest source. I wish this had been made more clear on MDC.

It appears there is a new hoop to jump through to build on Ubuntu 8.10. A better guide is on jboston's user page; consider this another way to skin a cat. I initially followed dbranski's guide to building Firefox on Ubuntu, though this doesn't appear to work on Ubuntu 8.10.
I grab some packages:

sudo apt-get install gcc g++ perl make cvs libxt-dev libidl0 libidl-dev libfreetype6 fontconfig libcurl4-openssl-dev libgtk2.0-dev libdbus-1-dev libdbus-glib-1-dev 

I grab a make file that lets me grab the source I'll need:

cvs -d :pserver:anonymous@cvs-mirror.mozilla.org:/cvsroot co mozilla/client.mk

I've also grabbed trace-malloc for this debug build, not sure if this is the right way, but it's what I've done. Skipped when not making a debug build.

cvs -d :pserver:anonymous@cvs-mirror.mozilla.org:/cvsroot co mozilla/tools/trace-malloc

I get into the mozilla folder, and open up the .mozconfig file to configure this build.

cd mozilla
nano .mozconfig

I paste the mozconfig for a debug build into the file (found the text from Mozilla QA's Howto Debug Builds). I comment out the CPU line and the let line beneath it, and the line marked MOZ_MAKE_FLAGS (the let line caused a complaint, and I don't care about the 'make' tool running jobs in parrallel). I then add the lines:

export CFLAGS="-U_FORTIFY_SOURCE"
export CXXFLAGS="-U_FORTIFY_SOURCE"

Then save the file. The above addition is because Ubuntu has changed the default gcc flags, and the fix is due to Ori Peleg. Unoptimised builds are not effected. If you're using an existing mozconfig that doesn't explicitly turn off optimisation, add the above U_FORTIFY_SOURCE statements.
I then get the source I need:

make -f client.mk checkout MOZ_CO_PROJECT=browser

And then start the build:

time make -f client.mk build

To find out if I'm leaking, I set an environment variable to a file I want to log to then run firefox (learnt from Mozilla QA leak testing):

export XPCOM_MEM_LEAK_LOG=~/leaklog0001.log
cd firefox-debug/dist/bin/
./firefox -P

When I've done whatever I want to test, I then quit Firefox and change the environment variable so I don't overwrite the log file.

export XPCOM_MEM_LEAK_LOG=~/leaklog0002.log

If I have leaks, the file tells me what objects weren't freed and in what quantity. To understand the output, I use MDC's debugging memory leaks page. It doesn't tell me why though, and that's my next problem.