The first thing to know is that the Frontier doesn't support the ICC profiles. The profiles possibly embeded in your file simply won't be considered. This doesn't mean that the Frontier does not manage at all the colors. It has a proprietary solution, with a simplified management compared to full ICC standards.

The Frontier has two main printing modes: "sRGB" and "Print Direct/no convert" ("PD"). The PD mode is pretty uncommon, most of the consumer/prosumer stores -if not all- use their Frontiers in the "sRGB" mode. The operators often know this latter one only. To get the PD mode, it's better to go to a small local store with its own machine, or to a pro store.

3.1 - The "Print Direct" (PD) mode

The file is actually supposed to be already in the Frontier native colorspace: it is therefore required to have the ICC profile of this colorspace,  in order to convert the files before sending them.

A generic ICC profile for the PD mode is available on request on the Fuji Europe site(see http://www.fujifilm.de/engl/serv/farbm_faq.html). If you contact me, I can also send it to you.

3.2 - The "sRGB" mode

In this mode, the files are supposed to be in the sRGB colorspace, which is the defacto standard for the consumer digital photography (even if  Adobe98 is often prefered by the prosumers). They are converted to the Frontier native space inside the Frontier itself.

The results are correct in terms of color fidelity, as long as the file are effectively prepared in sRGB. If they are not (if they are in Adobe98 for instance), they should be converted to sRGB before being sent.

The results are correct, yes, but not fully satifactory, with significant color shifts, mainly in the yellow and blue tones. Of course, since the native gamut does not contain the whole sRGB space, it is impossible to have prints perfectly identical to the files (this problem is very common on a vast majority on printing systems). However, I doubdt it can explain all of the observed shifts. In my opinion, a part of the problem comes from the internal conversion engine of the Frontier: we have no control over it (it is difficult to obtain such informations from Fuji), and it is a possibility that the algorithms do not fit all kinds of images.

Fortunately, it is possible to enhance the results when using the sRGB mode. This mode can indeed be considered like a "black box", which receives a file and outputs a print. What happens inside the box does not matter. If we have an ICC profile of this black box, it is valid to convert the files to this profile before sending them to the lab, trying various rendering intents and possibly various conversion engines, and retaining the combination that gives the "best" result. For this, the soft-proofing on the monitor gives a fairly good idea of the final (printed) result.

Indeed, the tests show that this method significantly enhances the fidelity of the prints. The main advantage is of course that we have the control over the conversion, instead of being tied to the Frontier internal conversion. It would in fact better stand to reason to work directly in the PD mode, but as stated previously, it is often difficult to find stores that use this mode in practice. 

A generic ICC profile for the "sRGB" mode can be downloaded from the Fuji Europe site, at http://www.fujifilm.de/eng/serv_1120.html. With this profile, we can check that, strangely, the "sRGB" mode doesn't use the whole Frontier native gamut, but rather the common part of this gamut and the sRGB's gamut.

3.3 - So what ? "sRGB" or PD ?

If you edit your pictures in the sRGB space and if you wish not convert your files before sending them to the lab, then the "sRGB" mode is the one to choose.

If you are willing to convert your files, then the PD mode is the most pertinent one: you have access to the entire Frontier native gamut. The only problem with this mode is its scarcity: only a local store with its own lab will eventually propose prints in this mode. The "sRGB" mode is hence often the only available solution, but it is a very acceptable compromise.