1280433 - Text / caret gets duplicated at jsfiddle.net

Status: RESOLVED DUPLICATE of bug 1277251

(Core :: Layout, defect)

Description

[Daniel Holbert [:dholbert]]

STR:
 1. Visit https://jsfiddle.net/
 2. Click in the "HTML" fancy-canvasy-textbox thing (the upper left one)
 3. Type a few characters (e.g. "a", and then "b", and then "c")

ACTUAL RESULTS:
After you type a character, an extra "ghost" version of it shows up as well, offset a bit.  After you stop typing for a second or two, the ghost versions disappear.

EXPECTED RESULTS:
No ghost versions.

I'm pretty sure this is a somewhat recent regression.
I'm using Nightly 50.0a1 (2016-06-15) with a fresh profile.

Comment 1

[Daniel Holbert [:dholbert]]

(Also, the blinky caret line gets duplicated towards the upper left.)

Comment 2

[Daniel Holbert [:dholbert]]

Attachment: screencast of bug

Here's a screencast of the bug, with latest Firefox nightly.

Comment 3

[Daniel Holbert [:dholbert]]

Range from mozregression:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=cc9051869d1a9078a821da5d1639299f9e836e0e&tochange=1ee604ae873ffae665e745b3553fb1c406dbdd6a

--> caused by Bug 1265237

Which helped me discover bug 1277251, which this is a dupe of (and which itself is a dupe of a more generic bug).  (Though,  bug 1277251 is tagged as e10s-specific, whereas I can reproduce versions of this bug in e10s as well as non-e10s profiles. I'll add a note about that on the other bug.)