If you select the hamburger menu in 20151119065326, and then mouse around its internal buttons, each button will be redrawn as the background (ie the underlying browser window) as you mouse over it.
Happens to me as well. Firefox Nightly x64 on Linux. Happens with my regular profile as well as with a new. I took a look at it and it appears version 2015-11-11 is the last one working as intended.
Appears to be fixed
Status: NEW → RESOLVED
Last Resolved: 2 years ago
Resolution: --- → FIXED
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