We were previously using an old version of the Mozilla updater before they
added Mozilla signature verification, but it's Intel-only, so we need to build
our own version of the current updater with signature verification disabled.
All declared Fluent files need to exist for a locale to be used (in a
window?). Since Mozilla code tries to load Fluent files, we need to copy
non-English Mozilla .ftl files to their default effective path (just in
the app omni.ja instead of the toolkit omni.ja).
Fixes#3094
