cursor position misalignment for Unicode characters

Maybe it depends on the browser font settings, but I experienced an issue with the cursor position in the editor for some Unicode characters, which does not look correctly calculated. For example:
```python
print('⚪⚪⚪⚪⚪⚪⚪⚪⚪⚪') # MEDIUM WHITE CIRCLE U+26AA
print('❎❎❎❎❎❎❎❎❎❎') # NEGATIVE SQUARED CROSS MARK U+274E
print('○○○○○○○○○○') # WHITE CIRCLE U+25CB
```
In Chrome/Edge, the cursor position is not correct for these characters (in all the three lines):
but somehow in Firefox the "WHITE CIRCLE"s in the last line are displayed correctly with (I think) a fixed-width font.

In the shell, I have no problem.