Not work for Firefox

[brushax]

Click button in Firefox is not working (even the demo page), but edge (maybe chrome) can work

[olucaslopes]

It's definitely not working. Click button uses the browser's Clipboard API to read the clipboard data and according to this documentation in Firefox, the user must explicitly enable this feature and also it appears to only support reading from the clipboard in browser extensions. It's good to mention too that the browsers require HTTPS to allow Clipboard API usage

I updated the docs in #3 to include this information about browser support