Sorry to say, you don't prune the NEW wood, you only prune the OLD wood. Forsythia blooms on year-old wood... which means the new shoots from this year will bloom next year. If you prune off your new shoots, you won't get diddly squat next year.
The rule goes: Once the flowers have faded, cut back 1/3 to 1/4 of the OLD wood, which is easy to recognize because it's not green like the new branches. Leave the new branches to grow, as they are the ones that will flower the following season.
"Forsythia form the next year's blossoms during the season after they bloom, in other words, during the late spring and early summer." is what I said, but I also said to cut off the green tips, Of course you're right, for forsythia that is blooming. I was mostly speaking about the old, neglected forsythia with few blooms.