From https://github.com/firefox-devtools/devtools-core/issues/1183
(thanks a lot to @brumm on the issue for providing all the info!)

STRs:

• open DevTools docked to the left
• resize the toolbox so that the tool overflow menu appears
• open the menu / close the menu
• zoom in DevTools (ctrl/cmd+plus)
• repeat the last two steps until the menu appears in the middle of the screen

Notes about reproducing the issue: from the investigations on Github, it seems that the issue only occurs:

• on non retina (non hidpi) screens
• with a dual (or triple) screen setup (logger has laptop_screen -> external_1 -> external_2)
• when the browser window is not too much on the right
• reported on both 70.0.1 and DevEdition 71
• it might also be macos only?
  (see the github issue for a bit more details)

It seems that the positioning logic is confused and thinks that the tooltip is on the left edge of the screen (as we can see the tooltip arrow is fully shifted to the left).

I am setting P3 for now due to the complexity of the STRs (and I haven't reproduced yet), but understanding the root cause might change that (if we realize this can also happen in less complex conditions)

overview of the setup used by the logger to trigger the issue (laptop screen hidpi, regular screen 1, regular screen 2)

Managed to reproduce it somehow on Firefox 70.0.1 on macOS Mojave 10.14.6 using 2 regular monitors. On an iMac (1980x1080) resolution and the other monitor is a Samsung monitor with 1080p resolution.

Attaching the correct screenshot.

Updating the flags since I encountered the same issue on Windows 10 with a similar dual monitor setup.
Something worth pointing out is that it also appeared to break with zoom_out not just zoom_in on DevTools.

I have the same issue but menu appears drastically in wrong place...

I have MacOS Catalina 10.15.2 and Firefox Nightly 74.0a1 (2020-01-21) (64-bit)

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Tested this on Win10, non-retina displa (two screens, one retina, one non-retina) and works for me.

Julian, should we close this one?

Honza

Can't reproduce either, let's close it. Thanks!