What is the installer task in Activity Monitor

My computer on boot up has 8GB of free HD space, its a Macbook Air 2011. Sometimes, not all the time, i get startup disk almost full, I look at the Disk utility and the 8GB has gone down to MB and eventually reaches zero. Fan is going crazy and it slows down.

I noticed a task called INSTALLER in Activity Monitor.

The only thing I ve done recently is install Firefox.

How can i find out what that Installer process is?