I have an Olympus TG3 and a firefly 2. The Olympus triggers the firefly but the flash misses the exposure, i.e. the flash fires after the shutter has closed (at least that's what I assume, I can't see it being too early). The TG3 makes no pre-flashes and I have tried the same set up with a different camera and it works OK. I am using a Yongnuo flash gun and I have tried just about every setting on the camera and flash and it makes no difference

Is anyone else using this set up, does it work?

I am tempted to think I need a Firefly 3 or a different flash gun but I would rather not buy something that is not going to solve the problem.

It sounds like you need a firefly 3.

I don't know the TG3, but almost all compact cameras fire a pre-flash, it may just happen so quick you can't see it.

Sometimes you can specify flash power (often in thirds for some reason). If you can, that sometimes stops any pre-flash, allow a firefly 2 to work.

What Yongnuo do you have? Some have a built in IR receiver...

Firefly 3 works ok with my TG4.

I use the TG2 and Firfly3 with reasonable results.

Thanks all, it looks like it's a firefly 3 then. Just for info the TG3 as various flash modes, Auto, Red-eye and Fill IIRC. I do not see any pre-flashes on Auto and Fill and I would not expect them on Fill which I is intended to provide fill-in flash on back-lit subjects generally.

I'll have to check if my Yongnuos have IR built in.

I have my TG2 flash set to Auto.

Big thanks to @Rob for the tip about the Yongnuo slave mode. It turns out that this works fine off the TG3 even with a piece of exposed film over the TG3 flash, so no need for a Firefly 

The other interesting finding is that the Yongnuo has several slave modes, one of which allows for pre-flashes. This  mode does not work with the TG3 in fill mode, so I can only assume that the TG3 does not fire a pre-flash which leaves me wondering what is going on with the Firefly.