Something else I've noticed: If you choose the "Maintain Layer Editability" option, Fireworks still sometimes chokes on the clipping mask, omitting important layers. To prevent this, and to preserve all the original Photoshop layers, try ungrouping the clipping mask inside Photoshop and re-saving the file before opening it up in Fireworks.
Simple clipping masks can be recreated in Fireworks by applying the bottom object as a mask to the objects above—for example, copying the bottom object and using the Paste As Mask command—choosing the "Alpha channel" or "Path outline" mask rendering option (i.e. not "Grayscale"). Depending on the objects involved, differences in rendering or blending between Photoshop and Fireworks may result in differences in appearance between the two versions. In that case, you might need to choose the "Maintain Photoshop Layer Appearance" option instead.
