Compress it more the first time. Re-optimising will add aditional artifacts to the JPEG. The best way to reduce the file size of a JPEG is to reduce the dimensions.
There's a great illustration at http://en.wikipedia.org/wiki/File:Quality_comparison_jpg_vs_saveforweb.jpg showing the effect and size of various levels of JPG compression using both Save as JPG and Save as Web.
That's for Photoshop rather than Fireworks reddog. Fireworks does a better job of compressing JPEGS than Photoshop.
Yes, but I thought it was a good illustration of the jpg process. Just curious as to why Fireworks does a better job of compressing JPG's than Photoshop?