Last modified: 2014-10-03 18:05:26 UTC
1. place cursor in large body of text in FF 2. Cursor up then down, everything is fine 3. Cursor right a dozen or so times, then up Then cursor jumps up and left to the same place it was after (2). Initial investigations show that disabling handling of up/down arrows makes no difference, but disabling handling of left/right does fix, so probably something to do with the surfaceObserver state?
Looks like a browser bug with Firefox's native selection having inconsistent state. I'm going to try poking some more at this tomorrow and maybe file some upstream bugs.
Minimal test case: http://jsfiddle.net/ybawstce/1/ (This will throw errors in some edge cases, but that's not the point; try arrowing around near the middle of the text.)
Calling nativeSelection.collapseToStart() seems to magically fix the erroneous behavior (http://jsfiddle.net/ybawstce/3/), we can probably use that as a workaround for selections that are already collapsed. (I see no neat way to fix non-collapsed ones; randomly calling some other Selection methods might help, but they probably won't be no-ops. These are a smaller problem anyway and can wait for Firefox to fix their bug.) I'm filing this upstream.
Upstream bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1075901
Change 164162 had a related patch set uploaded by Bartosz Dziewoński: ve.ce.Surface: Magic workaround for broken Firefox cursoring https://gerrit.wikimedia.org/r/164162
Change 164162 merged by jenkins-bot: ve.ce.Surface: Magic workaround for broken Firefox cursoring https://gerrit.wikimedia.org/r/164162
More "worked around" than actually fixed, but…
Workaround reverted, caused bug 71580 (ugly-looking "NS_ERROR_FAILURE" exceptions in some cases).
Possibly not anything we can actually fix…
