FRED Command Line Reference
From FreeSpace Wiki
Unless running from a command prompt, to use command lines, it is necessary to use a shortcut.
This command line option lets FRED display .jpg and .tga textures.
This option enables FRED to use glowmaps.
This option enables FRED to use specular highlights that is to use shinemaps.
Using this command line option, FRED2_Open will run in HTL mode.
Removes the various warnings displayed when FRED is not happy about a certain aspect of a mission. Only use this if you know what you're doing, as the warnings are there for a reason and ignoring them can in some cases lead to crashes during play.
The mod option allows FRED to work with mods, and functions exactly like the FS_Open equivalent. Multimods are possible as well, by separating the mods with a comma. For it to work properly, this has to be the last command line option.