I can always use help in that matchup too! Here's what I got
Falco can effectively shut down your shffl game from the right distance. If you stay totally grounded, always try to powershield that laser. I tent to get a couple PS'd laser against falcos, many of which are reflected, which helps create an opening for counter camp very well.
The grounded and short hop game is frustrating and seems more techincal. Against Falco (sometimes Fox) a full hop approach seems like the better choice. Gets you where you can breathe a bit, maybe pull a bomb, boomerang, cool zair etc..
In his face:
I'm a huuuge nair lover in 3.5. If you get near the full spacing of nair, landing a shffl'd nair or a late nair is great. On shield you can dash back safely after, jab, quick nair, tilt, grab. There's a lot of options but they're really all mixups. I like jabs on shield if they're at a safe distance.
You must not let Falco get back on stage. Getting good at grabbing the edge to bait out phantasms is big. Like from really high above the ledge, fastfall and get it. And predicting/seeing when it's coming onstage. Dtilt spike or fsmash bad firefalcos
Grabs at 0 on him seem near fatal. Not sure how confirmed the chaingrab is on him, but if you read/react to their DI on uthrow you should be able to get like 5/6 regrabs, followed but crazy Uthrow/Uair/Utilt combo, into UpB into edgegaurd type deally
For kills outside of combos I look for tricky nairs, jab-jab-dsmash, Dair depending stage? Maybe a good fair or nair coming from a full hop or double jump