Ok I take it you will have to do them.
This is where the acid content will etch into the plastic and leave heavy staining dependant on time, as the acid continues to etch until neutralized. So if the fire happen in the last few days it shouldn’t be too bad, if it happened 6 months ago, you will have a much harder job and may never get it out, always limit your quotes with fires to 7-14 days only but even that’s too long
The only way to get the staining out is to use a strong alkaline diluted in water first then used neat on the heavy stains You need to use at least a 11ph or higher, but not caustic to kill the smoke (which can remain active for years) and remove the deep staining.
There are a number of the high alkaline detergents out there (NOT SUGER SOAP) such as Strong Arm or Power Clean which we use all the time, even Prochem have one although theirs was originally developed to remove Tobacco Smoke it still works quite well
Always rinse well with CLEAN water and use gloves as your hands will dry out badly.
Perhaps you can ask Express, their sure to have one. However don’t get these chemicals on the glass especially neat as they will etch.
If you do (it is hard sometimes) just use a chrome polish like Solvo Auto from a car shop which will buff it out.
One of my lads got some on a £5000 dressing room mirror at a fire at the Albert Hall once an that stuff saved my rear end.
I have been dealing with commercial and domestic Fires and Floods for 25 years now full time.
Hope this helps.