1st u must go to the release 6 lvl 100 pokemon that which are third stage.... after u release!! u muz save game.. then u go to mosdeep city then go to the space centre then go in and talk to the guy which sae how many rocket launch.. then he will gave u a ticket. then u will be launch to space.. then u saw a deoxy.. it lvl 70.. it hard to catch. catch it wif master ball or ultra ball the best.. good luck...

mossdeep isnt in fire red sorry.
the only way u can catch deoxys is with an action replay or in a nintendo event where you get the aeon pass which lets you go to 7,8,9 and 10 island mew deoxys and oh-ho are there jicharys are also there:
my advice buy an action replay off ebay... nintendo event tickets are expensave and dont happen very often and if you live in the uk you'd have to go to america to do it.

don't listen to him don't release 6 lv 100 pokemon i have try but it didn't work

ya dont listen to him it doesnt work