The random map generator places "special" provinces which are indicated by icons. For firesite the symbol is the volcano. I see it as completely fair as long as your remember that special icons appearing on the map can be worth making a beeline for them, and for fighting over them when you get there.
Also, I guess that there is a list of possible sites that can appear in such a province of which 1 is selected. In one of my multiplayer games there are actually 3 volcano provinces under my control. 2 of them are the volcano site and 1 is the steel ovens.
Code:
"small" 1
"large" 2
"sea" 4
"somewater" 8
"mountain" 16
"swamp" 32
"waste" 64
"forest" 128
"farm" 256
"nostart" 512
"manysites" 1024
"deep" 2048
"cave" 4096
"firesite" 8192 - MAP SYMBOL= volcano
"airsite" 16384
"watersite" 32768
"earthsite" 65536
"astralsite" 131072
"deathsite" 262144
"naturesite" 524288
"bloodsite" 1048576
"priestsite" 2097152
"edgemount" 4194304
Hope this helps.