The preorders haven’t started yet, which I guess they just implemented by setting the stock to 0. Preorders open at the 1st of May at 9:00AM PST according to the product page.

On Android about:config is only available on the Firefox Beta and Firefox Nightly apps, not on any of the other versions.

Don’t know about 13, but I’m using it on 12 without issues. I mostly just block things though, so I’ve not tested spoofing data.

XPrivacyLua is no longer maintained YFI. It still seems to work just fine for now, but that probably won’t last. I’ve not found a good replacement for it yet.