I've enabled the New wikitext mode on Beta preferences, and it makes the "Edit source" mode unusable from Firefox on Android. The caret is shown at a different point to where the text is inserted (see images below). The same problem appears on Firefox Beta for Android.
I tried to edit article Strategies for Engineered Negligible Senescence, section Scientific controversy, and the following happens:
1) I tap in front of "Science fact..."
2) The window scrolls automatically to the top of the text area.
3) I scroll down to the paragraph I want to edit. The caret is shown where I tapped the screen (as seen in Image 1). But when I type "Example text", the text is entered here instead:
The interface has problems also when selecting text by long-pressing and dragging the finger; the drawn selection box is not vertically aligned with the text.