Comment 141 for bug 1711337

From what I can tell the maintainers have no intention of spending time supporting Ubuntu 16.04 or older. Even when Xenial was the current LTS they weren't responding here, and now that 18.04 has been out for 5 month there's even less motivation to handle older distros.

Having built Firefox 59 from source I think I get some of the reasons why they'd consider this a heavy support task. It's hard to get gcc and Rust to play nice on old cross-compiling toolchains, not to mention that sketchy assembly code for XPCOM. From a practical perspective, user workarounds can go in this order:

1) Use the latest firefox:armhf on 18.04 Bionic, if that's what you're running or you're open to upgrading.

2) Earlier distros like 16.04 or Debian Stretch: Install the latest firefox:arm64 if your system supports AArch64.

3) If armhf is the only option and you're on 16.04, you can still set up the firefox 18.04 deb package from Launchpad. Download its dependencies like libstdc++ and following my instructions in #117 to place the appropriate runtime-linked libraries.

Relying on armhf builds from Bionic in the worst case 3): this avoids having someone to maintain the whole build flow for Xenial and Trusty.

I'm only speaking for Firefox here, but if it all comes down to crashes in libxul.so then maybe much of this is sufficient for Thunderbird too.