ThingsYouNeedToKnow

When creating new tri-licensed files, please use the boilerplate from the MPL page rather than copy-pasting. This makes sure it's formatted correctly for automated tools.
If you work for any part of Mozilla in any capacity, the Initial Developer of the Original Code is "the Mozilla Foundation".
The MPL update will fix the boilerplate verbosity problem.
The Firefox icon files are now tri-licensed so official Firefox builds are fully free software.
You need let the licensing@mozilla.org team know before importing third party code into the tree. This is so we can check compatibility and meet our obligations under the licence.

If you need a new discussion forum in the Mozilla hierarchy, you can have one - just file a bug in mozilla.org / Newsgroups.
When filing bugs, set the OS and Platform to "All" unless you know the bug is OS- or Platform-specific.
When you produce a video, consider providing a transcript as part of production so people can make subtitles and then localize them for foreign and hearing impaired audiences.

When changing APIs, it is polite to check for uses of those APIs outside the tree you are focussed on, and let people know their code is about to break, even if you don't have time to fix it for them.
When you generate a file during the build, add the filename to the GARBAGE variable in the same Makefile.
The new commit access policy makes it really easy for you to set up a user Hg repo at Level 1 and get your friends to collaborate with you.
When you change the meaning of a string in a DTD or .properties file, you must also change its name. Otherwise, localizers won't know they have to re-localize it.