The main differences seem to be that -

 - the molotov is `$200 cheaper than the Incendiary Grenade`
 - the incendiary has a `faster deployment time`
 - the incendiary `can be thrown further`

Information from [here][1] and [here][2].

[https://www.youtube.com/watch?v=MbDkyndlQGk&feature=youtu.be][3]


  [1]: http://counterstrike.wikia.com/wiki/Molotov_cocktail
  [2]: http://counterstrike.wikia.com/wiki/Incendiary_grenade
  [3]: https://www.youtube.com/watch?v=MbDkyndlQGk&feature=youtu.be