I have Fireworks and when opening a background image, for instance, which is originally 2.55KB, if this image is saved with no changes, the size jumps to 35KB. If Optimize is set to PNG24, this may reduce the size by a couple KB.
But, hot to obtain the 2.55KB original file size???
Most likely this is happening because you are just saving the file instead of exporting it as a slice. When you simply save the file, it leaves all the layers, filters and other effects as data attached to the file (mostly so it can be opened later and re-edited). Creating a slice and exporting that slice, will embed that information and optimize it for better use.
Wage
"Everyone has to get knocked-down every once-in-a-while, otherwise you'll never learn how to get-back-up!
" A quote attributed to my Grandpa Wagers
Yep, but I only flattent the final image and then upload, I keep an unflattened version in a backup folder in case I need to edit it. Keeps loads time down a bit for our dial up friends.