Does not display the icons in the menu, if in *.desktop parameter Icon specified extension(.png). https://forum.xfce.org/viewtopic.php?id=9116
If you right click on the desktop does that icon appear in the menu? If so then it sounds like you've hit this bug: https://bugzilla.xfce.org/show_bug.cgi?id=10709
I don't think this is a bug in xfdesktop at all. I can reproduce it here using an out-of-spec desktop file (basically, add .png to the icon name in it) and indeed the icon no longer displays. However, you'll notice this: $ desktop-file-validate mozilla-firefox.desktop mozilla-firefox.desktop: error: (will be fatal in the future): value "firefox.png" for key "Icon" in group "Desktop Entry" is an icon name with an extension, but there should be no extension as described in the Icon Theme Specification if the value is not an absolute path
...and I just read the linked bug report. I agree that full path should be supported, but I'm not sure I agree with "fixing" things to work with "$name.$ext" - oh well :-) Thanks again, Eric, for what you're doing here.
Today I checked the patch http://bug-attachment.xfce.org/attachment.cgi?id=5395 works, just need to reboot. Thank you all!