Pumping the brakes is what I was doing when the pedal went to the floor!
The leak is most likely one of the rear lines above the fuel tank. Joy for that.
As far as lose of rear brakes effecting the fronts, well I've had it happen twice with the Grand Marquis before we had all new lines installed. Both times were rear line leaks and both times it could barely stop, although it didn't loose its braking power as fast as mine did. I mean I drove it 12 miles on a leaking line (topping the fluid off every so often) to the shop the first time. I think, but can't remember, I drove it very slowly to the shop 4 miles from here. This time all I did was move back and forth in the driveway a couple times and now it just barely stops from a crawl.
Luckily, there's now a shop right next door (he's a nice guy too), so I shop be able to limp it a few yards.
Really sucks though, I could swear when I looked at the lines (at least at the front of the under body) they were still silver and not rusty. I just hope it won't cost too much. No way I'm doing it myself. I hate working under the car (unless I had a lift).