.ProseMirror {
  position: relative;
}

.ProseMirror {
  word-wrap: break-word;
  white-space: pre-wrap;
  -webkit-font-variant-ligatures: none;
  font-variant-ligatures: none;
}

.ProseMirror pre {
  white-space: pre-wrap;
}

.ProseMirror li {
  position: relative;
}

.ProseMirror-hideselection *::selection { background: transparent; }
.ProseMirror-hideselection *::-moz-selection { background: transparent; }
.ProseMirror-hideselection { caret-color: transparent; }

.ProseMirror-selectednode {
  outline: 2px solid #8cf;
}

/* Make sure li selections wrap around markers */

li.ProseMirror-selectednode {
  outline: none;
}

li.ProseMirror-selectednode:after {
  content: "";
  position: absolute;
  left: -32px;
  right: -2px; top: -2px; bottom: -2px;
  border: 2px solid #8cf;
  pointer-events: none;
}

.ProseMirror {
  position: relative;
}

.ProseMirror {
  word-wrap: break-word;
  white-space: pre-wrap;
  -webkit-font-variant-ligatures: none;
  font-variant-ligatures: none;
  font-feature-settings: "liga" 0; /* the above doesn't seem to work in Edge */
}

.ProseMirror pre {
  white-space: pre-wrap;
}

.ProseMirror li {
  position: relative;
}

.ProseMirror-hideselection *::selection { background: transparent; }
.ProseMirror-hideselection *::-moz-selection { background: transparent; }
.ProseMirror-hideselection { caret-color: transparent; }

.ProseMirror-selectednode {
  outline: 2px solid #8cf;
}

/* Make sure li selections wrap around markers */

li.ProseMirror-selectednode {
  outline: none;
}

li.ProseMirror-selectednode:after {
  content: "";
  position: absolute;
  left: -32px;
  right: -2px; top: -2px; bottom: -2px;
  border: 2px solid #8cf;
  pointer-events: none;
}

Add another way to disable ligatures in Edge
Add another way to disable ligatures in Edge

FIX: The default prosemirror.css now also turns off ligatures in Edge.
