See gerrit 21142
The latest Firefox (Iceweasel) version shipped with the latest "working"[1] Debian is 10.x[2], so unless they install a newer Firefox manually, Debian desktop users can't use VisualEditor in Firefox.
[1] http://en.wikipedia.org/wiki/Debian#Additional_repositories
[2] http://packages.debian.org/search?keywords=iceweasel
Version: unspecified
Severity: normal