an image having blend mode as multiply,(its kind of reducing opacity) its showing its effect in adobe fireworks but its not showing the same effect,when overlapped on another image in browser.
Ah, okay. This is way more clear than your other phrasing of this same question.
The issue is that the graphics formats supported by browsers do not enable fancy layer-compositing like this. GIF files have a very simple one-color-is-clear transparency, and the PNG format allows you to specify an alpha channel, which is a simple degree-of-transparency per-pixel. There's no browser magic which allows an image file to act as a multiply layer.
This question is really off-topic here; here's the same question on Stack Overflow: https://stackoverflow.com/questions/2958813/how-to-replicate-ps-multiply-layer-mode , which basically is answered with "can't do it".
You may, however, be able kludge do it with SVG and HTML 5. SVG has an "feBlend" element which has a "multiply" mode, and the non-standard behavior described in that mozillazine link may make it work in some cases, or may make it into future standards. I wouldn't hold my breath, though. Best to find some other way to accomplish what you're trying to do.