Looked into this...
Latest Pale Moon is v15.
Wedge recently got rid of pre-16 support, which is when prefixes were dropped for gradients.
Hence, gradients don't show. :(
Fixed by downgrading requirement to v15.
Posted: January 14th, 2013, 02:31 PM
"The next major version of Pale Moon will be v19, to not fall behind too much in both graphics rendering engine and web standards support, even if this does not include h.264 video (which is planned for Firefox 20)."
(from website, this week.)
I'll update requirements when they do.