There are several reported results.
You will get another tree or moss
You get a moss dragon
The top five most common results of fire and moss dragons are:
Blue fire
probably a chrome
The most common results of are:crystalmountainsunmoonstormlavarainbowquakefireflyscorchair
You will get blue fire, or a storm.FireflyScorchSun or MoonStorm
There are a few possibilities. Those are Scorch, Firefly, or Lava.
Cold and fire dragons can not actually be bred directly together. You would have to use other combinations of dragons that contain these elements.
Possible results of fire + obsidian:LavaObsidianEmeraldCactusMotleyTreeAirSparkPoisonAbyssDouble Rainbow Dragon
The most common result would be an air dragon. There are many other results, but some of the more likely are salamander or coral dragons.
a scorch dragon is made by breeding the lightning and fire dragons.
Sorted from most to least common...CactusRainbowFireflyLichenStormPoisonSunMoonFlowerEvergreen
Cold and lava in the epic breeding island
You can get any of the following dragons, Mud, Obsidian, Ice, Iceberg, Snow, Rain, Blazing, Fog, Salamander, Lava, Glacier, Coral, River, Mountain, Smoke, Rainbow, And Double Rainbow Dragons