A few weeks ago armv7a Gingerbread-based B2G Gecko opt builds started running on most branches. As of a few hours ago we are now generating debug versions of these builds. We now have "Armv7a GB" rows for opt and debug with "Bg" (B2G Gecko Build) cells in them, and we'll add more build & test cells and platform rows as they arrive.
We know there's more B2G build requests coming, so as part of this, we also reworked our configs to make it easier to add additional B2G platforms and build types in the future.
For now, we've left the original "B2G" builds listed in the "Linux" row on TBPL. These are the initial opt builds that were set-up, and are exactly the same as the new Bg builds in the "Armv7a GB opt" row. This is transitional only - we'll be running them in parallel over the weekend and shutting the old builds off early next week after we're satisfied with the new ones.
For more details see bug 758425.