Quest for Vengeance - E: If this attack deals damage, the next attack you play this turn with a speed of 3 or less gets +2 speed.

Assuming I use the F on Feelings of Friendship (as long as it's in the card pool, attacks get -1 difficulty and +2 speed), if I enhance with QFV, my attack deals damage and I then play Chobi Jishi. CJ has a printed speed of 3, but because of FoF, this would now be a 5 speed attack, right? Meaning QFV would do nothing until I played an attack on the same turn which had a printed speed of 1 or less?

Unfortunatly for you QFV doesnt ask for printed and the static on FOFriendship will be applied before the speed boost of QFV at least that is how i would read it as FOfriendship doesnt look for anything and applys automaticly and qfv looks for the nmber i may be wrong but thats how i would rule it

Since those add 2 floating effect, when you play your attack you choose which effect resolve first, so you can choose QFV first, then FoF 2nd.

If you had 2 QfV however ( instead of 1 QfV and 1 FoF ), even if you could choose which one of the two resolve first ( irrevelant here ) only the first would apply it's bonus of speed, the 2nd would fizzle as the attack is no longer of speed 3 or less after the first bonus.

To clarify Zangetsu answer :

If Quest for Vengence was worded : R : after you play an attack of 3 speed or less [....]

Then you would be right.

BUT since it add a floating effect during the last played attack, right after you play the current attack, both QfV and FoF are floating effect, which resolve "simultaneously", but since simultaneously can't be effectively in this card game, then you choose which effect you resolve first because it is your turn.

If you choose QfV first, then FoF 2nd, both effect can resolve since FoF doesn't have any restriction.

If you choose FoF first for a unknown reason, then QfV cannot resolve as the played attack is not of speed 3 or less anymore ( except if the original attack was speed 1 )

I'd imagine so as as QfV is a floating effect that looks to resolve each time you play an attack.