Gas first openings still work exceptionally well in beating 1 gate FE builds. Protoss think MsC will keep them safe from early aggression, and tend to build very greedy. Do something like:
12 Refinery
14 Barracks
Factory, Marine when Barracks finishes.
Reactor on Barracks when you have 1 Marine.
Starport as soon as Factory finishes, make Hellions from Factory and Marines from the reactored rax.
Medivac as soon as Starport finishes.
When your Medivac pops out, load up your Marines (you'll have 7) and head for the opponent's base. You can also start your expansion at this point. Time it so you send your 3 Hellions into their natural at the same time you're dropping in their main. This build is very effective right now because most Protoss players delay starting warpgates a few seconds in favor of immediately starting their Mothership Core. You typically end up starting Starport construction at the same time they start warpgates research, which means your drop will arrive well before warpgates are finished, and you can do huge amounts of damage if not just kill them outright. They'll probably scout your Hellions headed for their base, but who cares? If they went 1 gate FE, they'll have 3 units at this point plus their MsC, which can't hope to fight what you just brought in. They'll have to pull probes to keep from dying which lets your Hellions massacre them.