STR: 1. Edit a test page on https://wiki.mozilla.org/ 2. Enter copy and paste many (dozens or more) lines of (very short, 2-3 characters?) text 3. Click in the middle of the lines of text 4. Hold down BACKSPACE and watch the text as many lines are deleted. RESULT: Lines of text either disappear until you start typing again or lines of garbage text are rendered on top of each other. This text corruption is very intermittent, but it seems to be a regression in Nightly 26 build 2013-09-05 or maybe 2013-09-04. The problem seems to be related to adding or removing lines of text and/or blank lines. The garbage text seems easier to reproduce in recent (2013-09-17) builds than the earlier builds.

Here is a screenshot of some garbage wiki text.

Looks to me like it could be related to bug 916751 (just landed on inbound). Please check whether it still occurs in builds with that patch.

This bug looks like a duplicate of bug 916751.