I just tried a div with a background image set to fixed + a gradient with transparent values and the image displays fine on mac
chrome Version 41.0.2272.89 (64-bit)
firefox 36.0.1
Safari 6.2.3 (8537.85.12.18)
Post an example if you are still experiencing the bug.
There is an ongoing bug with bg images not showing up. Not related with their fixed position or associated with a gradient., just they don’t show up. Re setting your image seems to fix it.