That is not to say that you cannot switch to a different icon for the test builds if you so choose once the test build is installed.
Understood. I have no GCC (and all other goodies) installed, so I didn't really look at code of nightly builds.
You cannot fully switch to a different icon. You can only override the icon of the WPS WPProgram object, but the icon in the top left corner (of the title bar) of FIREFOX.EXE is the embedded icon.
An example is attached. (Assigned) orange WPFolder object's icon, (assigned) orange WPProgram object icon, (embedded) blue title bar icon.
Dave Yeo doesn't have to install a complex mobile mountain data reflecting system to upload a new version with just a new icon at 1.2kbits/sec, but then I may want (to create) a matching blue WPFolder object too. Hence the question if this embedded icon was a new icon. I do prefer any of the usual orange icons, but I don't mind switching to a blue (folder) icon of possibly a last FF45.9 nightly build for i686 for OS/2.
Based on Dave's confirmation I may now create a blue planet folder icon, and use "our" blue planet icon as the new (default) icon. I.e. no assigned own, different, orange icons anymore. To replace the orange ones (mainly of the WPFolder object, the WPProgram object will use the embedded blue icon by default).