I have one of these 
 and have two buttons assigned to the mundane pageup and pagedown,  but two others to the backward/forward couplet which with e.g.a  web browser is working by default for switching tabs.
In this tiny patch I've added the two buttons for SciTE on Windows, usable with, e.g.
user.shortcuts=\
Backward|IDM_PREVFILE|\
Forward|IDM_NEXTFILE|\
P.S. I'll be working to speed up the SciTEKeys::ParseKeyCodesoon, having done some preliminary fiddling here. I'm no longer convinced that the speed-up factor is as dramatic, as stated, though. Also I want this function to be autogenerated in the future.
Cheers!
Committed as [3c67f6] with some simplification.
Related
Commit: [3c67f6]
Committed as [3c67f6] with some simplification.
Related
Commit: [3c67f6]