Make your background picture nicer:
Open irfanview
Choose File / Open to open your picture
To change the size of your picture: Choose Image / Resize and click 640 x 480 (or another)
To lighten your picture: Choose Image / enhance colors and play with brightness and contrast
When you are done: choose file / save and replace the file you had.
Close mozilla composer if it is open.
Reopen mozilla composer and look at your new background (format / page background)
You may also want to look for better background pictures:
www.grsites.com/