There was an attempt to remove it in bug 358128, but that was backed out
because of FTP listings, where e.g. a 'mozilla' link on the
ftp://ftp.mozilla.org/pub listing (without a trailing slash) would go to
ftp://ftp.mozilla.org/pubmozilla instead of ftp://ftp.mozilla.org/pub/mozilla.
It appears that versions of Firefox at the time of that bug wouldn't "redirect"
directories to the same url with a trailing slash when one was not provided.
It also appears that current versions of Firefox *do* "redirect" in such a way,
such that the <base href> is now unnecessary.
That <base href> prevents links from resource://... directory listings to work
properly because of security contraints added in bug 1184387, as they force
links to go to a jar/file url instead of the equivalent resource://... url,
which removing <base href> allows.
An explanation of the Mozilla Source Code Directory Structure and links to
project pages with documentation can be found at:
https://developer.mozilla.org/en/Mozilla_Source_Code_Directory_Structure
For information on how to build Mozilla from the source code, see:
http://developer.mozilla.org/en/docs/Build_Documentation
To have your bug fix / feature added to Mozilla, you should create a patch and
submit it to Bugzilla (https://bugzilla.mozilla.org). Instructions are at:
http://developer.mozilla.org/en/docs/Creating_a_patch
http://developer.mozilla.org/en/docs/Getting_your_patch_in_the_tree
If you have a question about developing Mozilla, and can't find the solution
on http://developer.mozilla.org, you can try asking your question in a
mozilla.* Usenet group, or on IRC at irc.mozilla.org. [The Mozilla news groups
are accessible on Google Groups, or news.mozilla.org with a NNTP reader.]
You can download nightly development builds from the Mozilla FTP server.
Keep in mind that nightly builds, which are used by Mozilla developers for
testing, may be buggy. Firefox nightlies, for example, can be found at:
https://archive.mozilla.org/pub/firefox/nightly/latest-mozilla-central/
- or -
http://nightly.mozilla.org/