STR:

1. Start with MOZ_ENABLE_WAYLAND=1 on Ubuntu 21.04.
2. Visit about:support.
3. Select a single word and drag it across the page.

Expected:

Cursor icon shows a grab hand without arrows and drop does nothing.

Actual:

Cursor grab icon shows arrows, dropping navigates as if text was a website. This navigation mode normally only occurs when dragging text from outside the page, like the address bar or an external application.

On xwayland the behavior is different, it gets stuck in navigation mode only after dragging over the address bar.

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=5d74bd11ae89329bc1eb8d437af89eb423e21ab0&tochange=11250511cdb8bfab7f1b061131a50335e9682bd0

Regressed by Bug 1730203.

Yes, I can reproduce it, Thanks.

It's because we set "drag accept" by default on Wayland as we anticipate that and leave D&D events to change it. Looks like about:support page does not set D&D status at all and we're in the initial 'accept' state here.

Fix window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=c73793adeb5bea50921f10765b65d4db6996fd3a&tochange=674e049eef29f5ed7d74e7bd35e943804458da95

Fixed by Bug 1767460.