I need one for all bands 25 - 1000 mhz
That will force you to use a minimal gain, but wide band antenna (works, but only OK throughout that range). Try the Austin Spectra (
Austin Spectra Mobile Antenna) since it covers VHF-Low through 800 bands. If you can live without good receiption on VHF-Low (30 - 60 MHz or so) consider the Larson Tri-band antenna (
Larsen NMO150/450/800 Tri Band VHF, UHF, 800 MHz Motorola Style Antenna | TESSCO). Both get pretty good reviews, but take care with screwing the Austin Spectra onto the mount as folks report issues with the tab on the NMO mount failing when screwing down the antenna (mostly due to the NMO Adjustment ring being missing or not properly adjusted).
Both of those antennas use a standard NMO mount (available for a drilled hole; trunk lip; "L bracket" for mounting by the hood, trunk, or other locations, magnetic mount, mirror mount, roof rack mount, multi-way adjustable mount, and who knows how many other variations). Using that type of a mount will allow you a wide selection of antennas should you decide to change it out later since many different antennas are made for it.
I believe that the firestick is a standard CB antenna and would work well for VHF-Low, but not so well as you move up in frequency. If you search around, you may find some antennas that use the 3/8 x 24 stud mount you talked about, but those would mostly be CB or HF Ham antennas and not much better than your firestick for scanning.
One thing to do at very low cost is to simply try the firestick to see how it works out (you may need an adapter to convert from the plug on your firestick to what's needed for your scanner, but that should only be a few bucks). If it gets you what you want, save your money for something else (like a down payment on a second scanner). If not, you'll know that the new antenna will probably be a good investment.
