I tried it on Firefox 79. The menu would show various emoji, but selecting one would sometimes use the Unicode version rather than the exact style that I selected.

For example, the laughing with tears emoji is in full color with an open mouth, but selecting it results in the outlined version without color and is showing teeth.

When the colored emoji do work, they will sometimes be cropped at the bottom or will leave some artifacts behind from a previous selection. These seem to disappear when switching to another tab and then coming back, though.

Some of the letters will extend beyond the boundaries of the image, too. For example, the left and right ends of the combinations "me" or "ww" get clipped off.

Despite those issues, this looks promising. I really like the interface and overall simplicity of the tool.