What tool or program would you recommend for learning touch typing on Linux?

I don’t have a particular recommendation, but in addition to local applications, there are also websites that you can try. The keyword you want to search for is “typing tutor”, e.g. on Debian.

For someone whose native language isn’t English, would you recommend learning on their native keyboard layout or switching to the US QWERTY layout for programming purposes?

For programming, the most important thing is that you can type the full set of characters present on US-QWERTY without too much acrobatics, because programming languages tend to use all/most of them.

Other than that it’s just down to your preference and comfort. I don’t recommend putting stock on any hype related to typing speed.

They’re switching their main repository from Mercurial to Git. Mozilla started using Mercurial before Git became de facto standard, but I imagine these days learning Mercurial is seen as an unnecessary obstacle for new contributors, hence the current switch.

As for why GitHub specifically, it’s because that’s where the rest of Mozilla’s projects already are. They have been using GitHub for a long time (14 years or more), with thousands of repositories there. It’s why Rust and Servo are on GitHub, for example.

Edit: See https://glandium.org/blog/?p=4346 for more thorough/accurate info.