You have have heard rumblings that FTP is going away...
Over the past few quarters we've been working to migrate our infrastructure off of the ageing "FTP"  system to Amazon S3.
We've maintained some backwards compatibility for the time being , so that current Firefox CI and release builds are still available via ftp.mozilla.org, or preferably, archive.mozilla.org since we don't support the ftp protocol any more!
How do I find my builds???
This is pretty big change, but we really think this will make it easier to find the builds you're looking for.
The Taskcluster Index allows us to attach multiple "routes" to a build job. Think of a route as a kind of hierarchical tag, or directory. Unlike regular directories, a build can be tagged with multiple routes, for example, according to the revision or buildid used.
A great tool for exploring the Taskcluster Index is the Indexed Artifact Browser
Here are some recent examples of nightly Firefox builds:
- The latest win64 nightly Firefox build is available via the
This same build (as of this writing) is also available via its revision:
Or the date:
The artifact browser is simply an interface on top of the index API. Using this API, you can also fetch files directly using wget, curl, python requests, etc.:
Similar routes exist for other platforms, for B2G and mobile, and for opt/debug variations. I encourage you to explore the gecko.v2 namespace, and see if it makes things easier for you to find what you're looking for! 
Can't find what you want in the index? Please let us know!