The "Sent!" ConfirmationHint that appears after sending a tab to another device is floating over the page content rather than being snug to its anchor button.

This could be fixed with some negative margin, however that then causes ConfirmationHints anchored in the urlbar to overlap their anchor (the Password saved! one for example).

There's some negative margins added to anchor the panels to the side of the button [1] but using a position of bottomleft instead of bottomcenter might make more sense. Similarly, there's 4px of margin on the on the .panel-arrowcontent [2] which maybe can't be removed but could help position things as expected.

The password ConfirmationHint is anchored to its image inside of the box that is the visual representation of the button, removing the extra margins and anchoring to the container fixes that hint and gets the send tab hint closer, but it is still below the hamburger menu since that button stretches all the way to the bottom of the toolbar row (its clickable padding is larger than the visual representation of the button).

Partly

[1] https://searchfox.org/mozilla-central/rev/72951aa826642f048da4c6b71b8b3e36a9606dcd/toolkit/themes/linux/global/popup.css#26-34
[2] https://searchfox.org/mozilla-central/rev/72951aa826642f048da4c6b71b8b3e36a9606dcd/toolkit/themes/linux/global/popup.css#43