I'm not a Makefile expert, but I don't think it was necessary. This file is used by additional-extensions.py to check if there is some new addon to installed.
https://github.com/ochameau/gaia/blob/97ef7dbd18060355e058deb441e1a1fe17e9f636/build/additional-extensions.py#L94
May be It would be clearer to execute `$(profile_folder)/installed-extensions.json" only when $(DESKTOP) is set?
```
$(PROFILE_FOLDER): multilocale applications-data preferences
ifeq ($(SIMULATOR),1)
  # Prevent installing external firefox helper addon for the simulator
else ifeq ($(DESKTOP),1)
  $(PROFILE_FOLDER): $(PROFILE_FOLDER)/installed-extensions.json
endif
```
Also, do you know if there is a easier pattern for doing `if ($DESKTOP && !$SIMULATOR)` in Makefile??