I have most of my music in WMA format and this is mostly working really well with Firefly and 2.5B10 firmware (on a M1001 Soundbridge).
I have found one album - only ONE out of about a dozen albums I've looked at - where the track order is displayed incorrectly by the combination of Firefly+Roku; all the other albums (all WMA) are displayed in the correct track order.
I am not sure what is "special" about this album, vs the others which are showing in correct order. When viewed in Windows Media Player or WinAMP, the track order is correct and the actual track tags look perfect. It has 39 tracks in it (rather more than any others I have looked at so far) and when I "show track info" on the Soundbridge when serving the album via Firefly, many/most of the tracks are showing up as being Track: 3" (rather than their actual track number, which may well be in the thirties range).
As I said above, I'm not sure why this one album would be a problem since its tags appear to be just fine (and no different from the albums which are showing in the correct order). I'm not sure what to do to narrow it down, but maybe someone else is seeing the same thing (on just some of their music) with Firefly and between us we can isolate it enough to get the bug fixed.