User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:89.0) Gecko/20100101 Firefox/89.0

Steps to reproduce:

1. Set "browser.proton.enabled to true" and "widget.macos.native-context-menus to true"
2. Launch Nightly
3. Open any page (e.g. https://www.mozilla.org/en-US/firefox/)
4. Open tab menu (control click the tab)
5. Click "Reload Tab"

Actual results:

The drag image blinks.

Expected results:

The drag image should not blink.

The Bugbug bot thinks this bug should belong to the 'Firefox::Menus' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Hi Eiichi,
I set up the config settings you mentioned but I am not particularly sure if I can't reproduce the issue or I am not looking at what I should.
Could you make a screen recording when you reproduce it and share it here?
Thanks!

For reference;
When I use Nightly, I always rename 'Firefox Nightly' to 'Namoroka'.
So the name of Application shows 'Namoroka' in the Screen Recording Movie.

When setting "widget.macos.native-context-menus" to "false", this issue doesn't happen.

This only happens after bug 1615732; turning off dom.event.treat_ctrl_click_as_right_click.disabled makes this problem go away. That pref is only set to true by default on nightly, so we won't have this issue in 89 release.

This bug can also lead to accidental tab detaches: Ctrl-click on the tab, and then dismiss the menu by doing a small drag gesture outside the menu over the content area. But, as Gijs said, only on Nightly.

Yeah, this looks like the Ctrl-click triggers a drag session, maybe we should prevent ctrl-click to start a drag session on Mac as it would bring up the context menu.

We have this piece of code to unset capturing content and :active state when the native menu opens, maybe we need something similar for aborting drag detection: https://searchfox.org/mozilla-central/rev/759872688df15a5d6ab305ffe39d90450590bfec/layout/xul/nsXULPopupManager.cpp#820-828

I now understand from comment 6 that this will not happen in release 89 given that dom.event.treat_ctrl_click_as_right_click.disabled won't be enabled on 89 but at some point later. Removing Proton tracking whiteboad items for this reason

I'm not sure if this is a good fix - basically, we want to cancel all effects from a mousedown.
A number of places call both ClearGlobalActiveContent and ReleaseCapturingContent. It seems like
all those places would be interested in canceling drag tracking as well.

The caller I care about for this particular bug is nsXULPopupManager::ShowPopupAsNativeMenu.

https://hg.mozilla.org/mozilla-central/rev/130f10069b56

Is this something we should consider for 91?

Probably not worth it - this only affects build with dom.event.treat_ctrl_click_as_right_click.disabled set to true, and that pref is only true by default on Nightly, not on Beta/Release.