"Drop here to hide": Unknown Unicode symbol

[LigH]

Under Windows 7 SP1, I only see a placeholder for Unicode symbol U+1F5D9 (Cancellation X); I seem to miss a font which provides this symbol.

[useranon]

I have this issue too. What feature is this supposed to be?

version 10.1.8.8
Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0

[LigH]

This seems to be a "drop zone" where you can drag&drop movable elements from a document, like images and videos.

[Giorgio Maone]

This seems to be a "drop zone" where you can drag&drop movable elements from a document, like images and videos.

No, it's a drop zone for the other buttons on the same strip, in order to let you customize the UI.

[Quest]

This was discussed long ago when this uni(que)-code gravestone appeared.
There were some problems with this (or whole menubar) then and at least one has survived:

When I run Firefox first time after rebooting the computer, the popup menu takes long time to appear (one time I measured 5 seconds). This is not a very big issue because it happens only then but still ...

[Giorgio Maone]

Please check latest development build, thanks.
v 10.1.8.9rc2
=============================================================
x Fixed externally handled resources opened in popups broken
by dynamic script injection (thanks rpr and paulmcg for
reporting)
x [Tor Browser, Linux] Replaced unicode glyphs not being
rendered on some browsers / platforms
x Prevent multiple canScript content messages during the same
page load

[LigH]

Yes, it displays a "Close" cross now. The position might be 2-3 px low, though.