v0.50 is faster than current Hatari versions (less accurate emulation often is faster).
Most likely Firebee is just too slow, but make sure you have the timer-d thing enabled and use frame-skip. On slower machines display updates can take a lot of time and Hatari may not have been built against the best performing SDL version.
Note that there are large differences between different programs, how heavy they're to emulate. If program does a lot of interrupts, that can be costly. If the emulated program is configurable, disable things like music, overscan etc, those generate a lot of interrupts & extra things that need to be emulated. After turning music off from games, you can also disable sound from Hatari (SDL thread for that can in some cases take a considerable chunk of CPU).