There are a few places to look for Mozilla L10n resources currently:
 - MLP: The Mozilla Localization Project
     is hosted on mozilla.org and contains a list of all major contributors to all languages supported on any
		 Mozilla version. There's a small howto, a page with various locale packs available for Mozilla, and
		 ftp.mozilla.org
		 hosts downloads for locale packs and localized Mozilla binaries.
		 (There are currently 89 L10n projects [excluding en-US] registered, 10 projects have released 1.3a versions,
		 30 have 1.2.1 available).
- MozillaTranslator: The MozillaTranslator tool
     has its own website, with a mini-howto (contributors to the documentation wanted!), downloads of
		 the tool itself as well as its source code, and a download page for language packs
		 (often a bit outdated though).
- Creating Applications with Mozilla: Chapter 11
     of the book about creating Mozilla applications (this chapter was written by Brian King)
		 is worth a look as well, esp. if you're writing your own application using the Mozilla framework
		 (I haven't come around to read it though).
- l10ntools: Finally, the new l10ntools MozDev project
     is currently built up and should contain a bunch of tools to deal with L10n work, some docs, and some
		 link to those other resources.
		 
 One subproject is mozpotools, which allows converting Mozilla's locale files to the GNU gettext
		 .po format, use the common translation tools for that format (KBabel etc.), and then convert the files back
		 to Mozilla's format.
 l10ntools will also provide XPI install scripts for use in a locale's installable XPI language packs,
     scripts for creating XPI packs from the .jar files that get exported by MozillaTranslator, and even
     scripts for creating localized binaries from the XPI file created above and an existing .tar.gz or .zip
		 binary Mozilla build, as well as some documentation about those tools and prbably general L10n issues.
		 Other useful tools will probably be added if people give them to us.
In the future, 
l10ntools should have link to all those resources (or host them theirselves).