I have one of these panels in my house. I believe it was installed in
1962. I've load tested all of the breakers to see if they trip on
overload. They all do. Some newer breakers made in the 1980's do trip
faster though, but that would be the case for any brand (the newer ones
had white marking instead of red on the handle). The only one I had
that failed was a two pole breaker that was really two single pole
breakers ganged togather. I separated them and they tested and work
fine as single pole breakers (and I would trust two single pole
breakers ganged togather with a piece of metal anyway). Having said
all of this, I would be highly suspicious of any old FPE 2 pole
breakers. No real need to replace the whole panel if you can get new
breakers cheap enough. They charge an arm and a leg around here for a
new panel install (they don't allow DIY). The new breakers from Canada
are perfectly fine. Not sure where you can find those (I got one off
eBay).