User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/114.0

Steps to reproduce:

I am using KDE Plasma 5.27.6 in Kubuntu 23.04 and Firefox Snap (Wayland session).

When I drag and drop a file from Dolphin to Firefox (f.i. a PDF file to open in Firefox), it works as expected in the first time. But in the second time I do it (f.i. dragging another PDF file into Firefox), it no longer works.

This problem also happens when dragging and dropping files to websites (f.i. Moodle, Whatsapp Web, etc). If I close and reopen Firefox, it works again.

I am not sure whether this is a Firefox bug, or if it is KDE Wayland at fault here. It could even be Dolphin to blame, but I can't tell. Switching to X11 makes the problem go away.

Can someone else confirm this issue?

Actual results:

Drag and drop a file from Dolphin into Firefox stops working in the second attempt.

Expected results:

Drag and drop should remain working.

The Bugbug bot thinks this bug should belong to the 'Core::Widget: Gtk' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

UserAgent: Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/116.0

I can reproduce the issue with Firefox 116 in ArchLinux using Gnome Shell 44.3 (and also with older Firefox versions, at least since 112).

• Under X11, everything works fine. If you drag and drop a file to the Firefox frame (tab bar, address bar, new tab...), Firefox opens that file. If you drag and drop a file into a website it does what it is supposed to do.
• Under Wayland (with MOZ_ENABLE_WAYLAND=1), dragging a file into a website or the rest of the browser causes the mouse icon to loop crazily between a hand and a hand with a question mark. In the best case, nothing happens when the file is dropped. Otherwise, Firefox crashes and prints this message on the terminal:

  [GFX1-]: Wayland protocol error: unknown object (4278190080), message error(ous)
  Gdk-Message: 15:12:48.037: Error reading events from display: Invalid argument
  

  The crash sometimes happens at the first attempt, but usually after one or more.
• Under Xwayland (in a Wayland session, but without setting MOZ_ENABLE_WAYLAND), it may or may not work, apparently under the same circumstances. Moreover, when it does, dragging causes the browser to start iterating over the elements of the website as if the tab key was continuously pressed, which makes difficult to drop the file in the appropriate place. When it does not work, the mouse icon does not change and nothing happens.

Drag and drop works works fine with Chromium under Wayland, so the problem seems to be related to Firefox rather than to the other side.

This may be unrelated, because it appears with X11 too, but this message is printed on the terminal at startup:

[GFX1-]: vaapitest: ERROR
[GFX1-]: vaapitest: VA-API test failed: failed to initialise VAAPI connection.

The bug reports #1791431 and #1651347 seem to be related to this one.

I attach Firefox's output to the terminal before the crash with WAYLAND_DEBUG enabled.