OK, so the Firefly has "rapid wind down travel adjustment?" That is important, and you may be alright after all. Manitou has two basic travel adjust systems (for 04 anyway): rapid travel adjust, and travel wind down. The rapid adjust is a sort of catch which stops the fork from reextending after it has compressed past a certain point. This keeps the fork a few inches down in its travel. It can still compress further but not reextend to its normal full length. The fork's spring is heavily preloaded at that locked down setting, so initial movement is very stiff. It may be ok for climbing, but NOT for normal all-around riding. When I demoed the Minute 3:00, I did not care for this feature, especially since the knob was at the bottom (!) of the fork leg. How dumb is that? The Sherman Breakout Plus I demoed also had the TA system, but the knob was on top. A little better.
The travel wind down I tried on the Minute 1:00 was another critter entirely. You can set the travel at any point between 100 and 130mm and the spring rate does not change. The SPV chamber pressure may increase a bit, but this was not very noticeable. Cranking the fork down did not diminish the fork's rideability at all. This is similar to Fox's Talas feature. Very nice.
If the Firefly really does have the travel wind down feature, try it out. If it has the rapid travel adjust, I'd dump that thing. Either way if it is too much fork for the bike, someone here will GLADLY take it off your hands. It would be a super nice upgrade for a 5-Spot.
If you need a new fork ASAP, look at the new Floats (lightest), a Talas (medium weight), or the Minute 1:00 (coil fork). Larry (Ventanarama) just got some of the new Fox forks in. Call him up. I think the Minute is on sale in a few places. Not sure...
My $0.02