I was wondering if it works alright to replace a tiagra 9speed front derailleur on a 50/39/30T triple chainring set with a 105 10speed triple front derailleur ( https://www.chainreactioncycles.com/M...?ModelID=30966 ). I have a 105 9 speed in the rear and a 9 speed chain.

What do you guys think?

Thanks!

Can you offer more information about the crankset and chainrings? Your chainring sizes make it sound as if you have a 10-speed or aftermarket crankset. All Shimano 9-speed road triples except Dura-Ace came equipped with 52-42-30 chainrings.
A 10-speed 105 front derailleur should fit your chainrings OK because they are the same size as a 10-speed 105 crankset.
I'm thinking that the 10-speed derailleur may have a slightly narrower cage and could cause a bit more chainrub. I suspect you could replace the 9-speed chain with a 10-speed chain, at least this seems to work in some cases. Unfortunately this may be a "try it and see" situation.

Woops, sorry the chainring numbers was a typo.

The crank is a fsa vero with 52/42/30

I don't think it will clear your 42T ring when shifting to the large ring.

... because?

Check the specs for the 105 FD. It should say max chain ring difference. That should give you an indication of clearance.

You'd have better luck with a 9-speed Shimano triple FD, but not D-A.