Created attachment 8485189 [details] screenshot STR: 1. Create a new profile, and within a few seconds of starting Firefox, open a new tab page. ACTUAL RESULTS: See screenshot -- the "What is this page?" popup has a weird white border, offset a bit from the dialog, stomping over some tiles
35.0a1 (2014-09-05) Mozilla/5.0 (X11; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0
The screenshot attachment 8483381 [details] from bug 1062210 seems to have the mysterious border filled in with the contents of the previous view -- the welcome to firefox page with the ui tour? Also from the other bug: "This is a Linux specific issue, I couldn't reproduce it neither using Mac OS X 10.8.5 nor Windows 7 64bit."
With bug 1062256 fixed for tomorrow's Nightly, this may be avoided because there's no longer two panels open. I'm assuming the bug doesn't manifest if there's just one panel as the top right one with the menu seems to appear without the mysterious border. If someone can test tomorrow or grab a tinderbox build now: http://ftp.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/fx-team-linux64/latest/firefox-35.0a1.en-US.linux-x86_64.tar.bz2
Not seeing this anymore. Marking WFM, thanks!