Created attachment 8878707 [details] Screenshot See attached screenshot. There are two weird things: - The blank space under the search engine icons. - The line below the icons only goes through half of the popup. This doesn't happen with a new profile. I wish I could use the browser toolbox inspector, but when I hack things up (thanks to _6a68 for a one-liner) to get the popup to stay put, I can't use the browser toolbox for mouse focus issues. Now, for the fun part: now that I'm filing this bug, it's not happening anymore in the window where I'm typing this. However, I do have another window open in the same session that still has the problem, and if I open a new window, it has the problem too. This is on beta, btw.
This happens irrelevant of the popup width, although with a narrower popup, the location of the settings button becomes weird (not always on the rightmost end). And now that I'm observing this, the offsets are looking suspiciously related to the witdh of the tabbar that I have on the left through tab center... and yes, disabling tab center fixes it. Reenabling tab center, though, doesn't make it happen again.
Mike says that this is related to sidebars "that move the main toolbar." I didn't know that that was a thing. Depending on how that works, it's probably screwing up how we cache the one-offs, and how we invalidate that cache. The problem does not happen with the built-in sidebars. In addition to Tab Center, Mike also says that this happened when he used sidebar-tabs and tabcenter-redux. I'll mark this as P3 for now since you need add-ons to reproduce it, but feel free to bump it up. Needs investigation.
Priority: -- → P3
The Tab Center page (https://testpilot.firefox.com/experiments/tab-center) has this text on top: "Firefox is changing fast. Tab Center may have bugs in Firefox 55 and will be disabled completely in Firefox 56+." sidebar-tabs seems to be in the same situation. We should focus our debugging on tabcenter-redux which at least seems to be using future-proof APIs. Then again, its user base is tiny, so I agree that P3 is the right priority here.
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