As long as you accept that you'll have a poor/limited/obstructed view of both shows, I do think it's possible to see both fireworks and WoC on the same night.
I don't really think there is anyway you'll be able to see the
first showing of WoC and fireworks. WoC has a run time of 25+ minutes, which would only leave you only a few minutes (in a perfect world) to get out of the WoC viewing area, out of DCA, into DL, and to a spot where you can see the fireworks. I suppose it's possible, but it would pretty tight. I've done this once (kind of) and fireworks started while we still trying to get out of DCA (the crowds make it hard to move fast) and we finally made it into DL about half way through fireworks.
Most folks that have talked about seeing both shows, typically try for the second WoC (you'll need a FP because the show time is after the park closes, but if you have a FP they usually will let you into DCA if you don't make it to turnstiles by 10:00 pm - I haven't tried this personally, but that's what I've read). I recommend watching fireworks as close to the exit of
Disneyland as possible, then immediately heading over to DCA. Remember has a run time of 16 minutes, so that should give you just enough time to make it over to DCA (assuming fireworks starts on time, but they can delay it if the weather is no cooperating and they think the winds might improve), but you'll probably end up in the back of the WoC viewing area with a very poor view.
