Well, yes, that's odd.
Your FW .gif has 58 colors. If I open your .png and use Image Preview to export, selecting Exact for the palette, I get 100 colors. Looks like that's what you get going through PS. I don't know what to tell you. If you have more than 256, then FW will fall back to Adaptive, but will usually not give you 256 colors, but something much less. Hmm...if I go for the Adaptive palette, I get 64.
As for GIF vs. PNG.... The .gif file I got is 2.12k. That seems pretty good, but if I export as a 24-bit PNG, the file is 470 bytes. Not kbytes, bytes. That's a factor of more than four!
The problematic PNG is the 32-bit format. You can use the 24-bit format just fine. The 8-bit PNG is also fine, but I think you'd run into the same color problem.
Thanks, it's nice to know I'm not nuts for having the problem. And if
24-bit PNG is OK for all browsers, that will work just fine. It does
seem to be what FW wants to do by default.
Nope, you're not nuts!
Yes, 24-bit PNG is good for all but the really old browsers. The 8-bit PNG is good for when you need a semi-transparent image (see http://www.sitepoint.com/blogs/2007/09/18/png8-the-clear-winner/).
With any indexed palette that gives you less than 256 colors, you can manually add more, but it's a pain.
Here's a great tip I picked up from this forum.... Since the FW document is a .png it can be easy to overwrite your working document with a flattened version. To keep track of what type of .png file you have, FW or flattened, give your FW documents the "extension" .fw.png (the .fw is really part of the file's name) and your flattened exports the simpler .png.
Use JPEG format for gradients.
Nope. The gradients work fine in .gif from photoshop and .gif is the
preferred format for exporting vector art. Also, we need to constrain
some of the pixels to exact hex values, which jpg doesn't do. It's a
series of buttons, and if we export as jpg, the colors vary slightly
across the set.