User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:55.0) Gecko/20100101 Firefox/55.0 Build ID: 20170824053622 Steps to reproduce: Attempted to customize toolbars. When opened customization, new tab button appears on tab bar (+ sign). I can move it off of tab bar to customization menu and/or back to tab bar. However when closing customization, the new tab button always disappears. I have Firefox 55 32 bit version on a 64 bit Windows 10 desktop.
Do you have any add-ons installed? Can you reproduce with a clean profile? On the profile where this is broken, if you do the following: - open about:config - search for "devtools.chrome.enabled" - switch it to true by double-clicking that line - hit ctrl-shift-j to open the browser console - evaluate: CustomizableUI.getWidgetIdsInArea("TabsToolbar") what is the output? This feels like bug 1370791.
Without more details this shouldn't be a p1. I'll check on bug 1370791 though.
status-firefox57: --- → fix-optional
Priority: -- → P3
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