The `restore()` function does not correctly set neither the caret position nor selection by code

[angezid]

This is not related only to FireFox!

See a demo of this bug and result of fixing: bug-demo.zip

...
const { anchorOffset, focusOffset } = getSelection(),
    // detects setting selection by code and deletion at the beginning of text node
    greaterThan = pos.start !== pos.end || anchorOffset === 0 && focusOffset === 0;

visit(editor, el => {
    if (el.nodeType !== Node.TEXT_NODE) return;
    const len = (el.nodeValue || '').length;

    if ( !greaterThan && current + len >= pos.start || greaterThan && current + len > pos.start) {
        if ( !startNode) {
            startNode = el;
            startOffset = pos.start - current;
        }
        if (current + len >= pos.end) {
            endNode = el;
            endOffset = pos.end - current;
            return 'stop';
        }
    }
    current += len;
});
...

For the pos.end the comparison should always be >=.

For the pos.start the comparisons should be:

• for typing or deleting end character of a text node - >=
• for programmatic selection - >
• for deleting the start character of a text node or range that started at the beginning of a text node - >

The two conditions are used to switch necessary comparison:

• pos.start !== pos.end detects programmatic selection
• anchorOffset === 0 && focusOffset === 0 detects deletion at the start of a text node

It won't fix open #111 and #115 issues. I was messed up with testing related to the issues.

By the way, maybe it worthwhile adding if (typeof highlight === 'function') highlight(editor, pos)? It removes dependency on highlighting plugin.