User Agent: Mozilla/5.0 (Windows NT 6.1; rv:16.0) Gecko/16.0 Firefox/16.0 Build ID: 20120626030539 Steps to reproduce: I have Nightly and RTM on my Android device. However, I'm now unable to send pages from RTM (14) to Fennec or vice versa.

You can't sync multiple Fennecs on the same device.

P5: won't be directly addressed; see Bug 761206, which will take care of this.

This is essentially in place now that much of the work for Bug 761206 (specifically, Bug 772645) has landed. The user experience is not great, since we don't sync aggressively enough to make this feel instantaneous, but Bug 763021 goes a lot of the way to making this better. We could improve the user experience a little by broadcasting to other Firefox versions installed on the phone that some Firefox Sync action has happened and they should Sync as soon as possible, but that's a different concern.

This is fixed, should I file a followup for pinging other installations on the same device upon sync?

Sure, thanks Paul.

This should be either marked FIXED or marked as a dupe of bug 1098303

I think Comment 3 explains the situation.