you will need to change ~user~ to you username, eg madnessred. If you are unsure please look at the bottom of this post for an alternative mthod to find it out.
2 - Once you have got your launcher details right click on a png file, slect "Open with > Open with other application"
3 - Where it says "|> Use a custom command", click that
4 - A box will appear, in that paste the custom launcher information and press open. Now fireworks will open with that file. Clsoe fireworks. Now when you double lick to open a png it will open with fireowrks.
How to find out your fireworks launcher information
1 - Right click on the fireworks icon in the Applications Menu (For me Applications > Wine > Programs > Macromedia > Macromedia Fireworks 8
2 - Select add launcher to desktop
3 - Right click on the Fireworks Icon, select properties, select the launcher tab.
4 - Where it says command, copy the text from that box, that is you launcher information.