Ran into a curious issue playing OpenXCom 7.5.3, XPirtaez M5.2.1. Simply put, the fire extinguisher code does not seem to be working properly.
Simply put, while fire extinguishers in weapon form (i.e. item with aimed shot cloud and limited ammo) work as intended, putting the isFireExtinguisher effect into an instant grenade like XPiratez' foam grenade does not work properly - while they put out ambient fires, burning people keep burning.
Frustratingly, this issue was not present in OpenXCom 7.0, when I played XPiratez L10.
In XPiratez, this has some implication to mid-lategame play - advanced weapons start a lot of fires and being able to quickly put out burning soldiers becomes important. Needless to say, an ethereal battleship is not a good place to find out your premier tool do this doesn't work.
To make things even weirder, changing the item to behave like a normal grenade does fix the issue. But I would prefer not to resort to this.
Made a few screenshots to illustrate the issue. In order - after lighting the test craft on fire, before throwing foam grenade, after throwing foam grenade, after using fire extinguisher.