Hi, I'm a member of the mobile Firefox team at Mozilla. Building for ARMv7-only lets us use the Thumb-2 instruction set, which results in code that is smaller,

Hi, I'm a member of the mobile Firefox team at Mozilla. Building for ARMv7-only lets us use the Thumb-2 instruction set, which results in code that is smaller, faster, and uses less memory. We used to have ARMv6 builds available, but at this point the browser is not really optimized enough to run well on older (or low-end) devices. And since we were not actively testing or supporting those builds, the code now has some crashing bugs (probably related to the JavaScript JIT) that show up only on ARMv6 builds. Without fixing those bugs, you can't actually run Firefox on ARMv6. We continue to reduce memory and CPU usage, and if it it gets good enough to support these devices then we might start working on it for a future version.