Hi
The 'Orange stains' are actually putrified body fats that have built up over time.
I have found the best thing for this is Detox Mould & Mildew Remover.
Make sure you ventilate if possible, spray on and leave for 5-10 mins, go back spray on again and leave it again. Most of it should now be gone and you can use a toothbrush and scrub off the stubborn bits, then when finished rinse off and buff up with glass cleaner & kitchen towl.
IF? you are going to use Harpic PLEASE do NOT mix with the detox or any bleach, it produces a chlorine gas and is very dangerous and toxic, Chlorine gas is mustard gas which was used in the 1st WW.
Regards
Martin