Firelance is a very powerful alien weapon that can only be acquired after a "U.F.O. random encounter" is triggered. There is a way to trigger this encounter at the very beginning of the game.

1) go to whilem's wharf.
2) save on the pier closest to the shack.
3) to the east near anchorage memorial is one of many places that trigger random encounters.
4) swin across the waters , to east , towards anchorage memortial.
5) looking at the map on your pip-boy , you should see and island where anchorage memorial is situated. On the very western edge of this island , where there is a stone straicase , is where the random encounter is triggered , swin there.
6) look to the sky (preferably during daylight) and look for and explosion , if nothing happens then re-load your saved game. (be prepared to re-load a half a dozen times)
7) if the explosion is triggered then simply go look for the weapon , there are also 24 power alien cells that drop from the crash.
8) with this powerful alien weapon , the early part of the game is extremely easy. Go do some questing.

NOTE:

it is very important to save before crossing the river , otherwise you might receive a different random encounter or simply nothing at all. With a little patience you will eventually get it , it took me 7 re-loads , on the 8th try the explosion was triggered.

the explosion is very easy to see in daylight , you will see a long trail of black smoke in the sky , followed by a loud bang , and an explosion in the sky. You will probably see the weapon fall as well.

firelance desintegrates rather quickly compared to other weapons , but even at poor conditions it is still much more powerful than other weapons at early levels.

coupled with the "alien blaster" you should breeze through the early half of this game.

Dogmeat can also be used to retrieve "firelance" and the alien power cells.