my microwave had a fire (food) can i still use it

gold star wave plus II  - model # ms-139sc

As long as the fire was contained within the walls of the heating
compartment, and did not travel through the fan duct, the microwave
should be safe to continue using.  You may be able to visually inspect
the fan-blades to ensure they are not melted.  This would be the only
danger.  Also inspect the door seals to ensure they are not melted.

You say it was a food fire -- might this be connected with your other post? 

If however you only assumed it was a food fire because of flames and
sparks, (perfectly reasonable) but was in fact something else, the
usual cause is carbonisation of food residue on the ?waveguide cover?.
Bit like a mini Dante?s Inferno. Thin mica composition or plastic
plate a few inches across, inside. Cure is very simple -- often the
blackened area can just be scraped back down to un-charred mica (or
plastic). Failing that, replacement covers are very cheap, usually
easily removed, being held in with a push-pin or simply slotted into
place.

It is wise to ensure that this plate is regularly vigorously cleaned
-- very common for them to fail. Its function is only to prevent food
and fumes entering the waveguide and is not a critical component as
such.

Best