What I said is that the old Chrome model, wherein the official binaries ship H.264 and have a paid-for license, if adopted by Firefox, would have meant two things, as I understand:
1) If someone wants to take the Mozilla binaries and redistribute them (possibly with some simple changes like a different default theme or a default preferences file that whitelists some intranet sites or whatever) they have to pay for an H.264 license. Things like copying Firefox from your computer to your friend's computer would need you to have an H.264 encoder license, since you're creating a new encoder (now it happens that the license fee for that level of distribution is 0, so you're actually ok; just don't put that modified package on a public web site).
2) If someone wants to fork the Mozilla codebase and build a browser with equivalent functionality and distribute it, they have to pay for an H.264 license.
#2 there is precisely what GPLv3 is intended to prevent, by the way. Mozilla is licensed under GPLv2, so this would be within the letter of the license, but arguably not the spirit. Certainly we felt that it would not be within the spirit.
It is perfectly 100% legal to distribute uncompiled source code without a license to any related patents. After all, it's a description of the patented machine and not the machine itself, much like an ideal patent application. Where you run into trouble is distributing the compiled binaries, the actual machines covered by patents.
You can get into no trouble at all over source tarballs of ffmpeg, but Debian is deathly afraid of hosting usefully-compiled debs of it in their repositories for a reason.