Download AArch64 version of xulrunner

[yuyichao]

AFAICT mozilla still don't provide aarch64 binary on linux and this is the first/only place I found that provide the firefox binary for the same version used on other platforms. Feel free to suggest other download sources...

This is the main change I needed to produce a working package for aarch64. Once zotero/cross-xpdf#1 or equivalent of it is merged and deployed, the rest of the changes should be really simple (if we accept leaving the updater broken for aarch64).

[dstillman]

Where is that linked from?

If we're going to distribute something, we really need it to come from a more official URL.

[yuyichao]

It’s from Mozilla team ppa: https://answers.launchpad.net/~mozillateam/+archive/ubuntu/ppa/+build/17514808.

[dstillman]

But is that linked from somewhere? Discussed somewhere? We just can't bundle something that's not documented as an official release.

[yuyichao]

As I mentioned, mozilla does not provide an aarch64 download link so I doubt there's an official binary for that.

What do you mean by "discussed somewhere"? Do you mean if there's some messages from mozilla that proves the officialness of that ppa or some discussion regarding it before I made this PR?

If it's the former, I don't know and I think the PPA is more official ubuntu than official mozilla anyway. This is the only one I can find. I find it convincing enough (also see below) since it is actively maintained and has been around for a long time. They also have their ubuntu wiki page (https://wiki.ubuntu.com/MozillaTeam) but I guess that doesn't mean much either (it doesn't mean anything more than the repo itself to me at least)

If it's the latter, then I guess this PR is the discussion. I wasn't sure if this source is good enough so I wasn't going to submit this before you encouraged me to do so on the forum. (note that this is exactly the link I pasted on the forum in my original post). Given that I don't believe an official build similar to the ones for x86 is ever going to happen for this release (60.9.0esr, or any releases to-date FWIW), which one(s) of the following, if any, do you think would be an acceptable method then,

1. Official distribution packages (this PPA is fairly close IMO and I wasn't able to find anything this old elsewhere...)
2. Convince you that the ubuntu mozilla team is trust worthy (for me, an active PPA with long history is convincing enough)
3. Automatic custom build via CI (not sure if github action is powerful enough to build firefox though)
4. Manual custom build by someone you trust
5. Any other methods?