Per <https://github.com/whatwg/compat/issues/18>, everyone supports -webkit-text-size-adjust already, and it is very unlikely that the unprefixed version would be able to behave any differently. We probably should have done this before taking the webkit-prefixed version.
There's also https://drafts.csswg.org/css-size-adjust/ although we're moving towards maybe removing the feature; I don't think it's enabled anymore, although I might be wrong.
by removing the feature, I mean removing font inflation, which is what text-size-adjust affects
Fennec turned off automatic font-inflation in 39 in Bug 1127441, but b2g still uses it: https://dxr.mozilla.org/mozilla-central/source/b2g/app/b2g.js#861 If the plan is to remove automatic font inflation, then I suppose it doesn't make sense to keep the ability to disable it via (-moz-|-webkit-|unprefixed)text-size-adjust, unless we find that pages are using that to adjust to a specific non-disabled value (something other than 100% or none, right? Based on a quick glance at GitHub usage, every token property value on the handful of pages I looked at is either `100%` or `none` -- but that's not representative of the web. Does text-size-adjust have any effect on Desktop?
It doesn't have any effect on Desktop. We also never added support for a % value; we only support 'auto' or 'none'. I'd like to understand a little better why it was disabled on Android before we start ripping stuff out, though. I still think font inflation is important for getting to older content on the Web, or content designed without consideration of mobile.