The QR Code Extension

Generates a QR Code from the Page URL of the current tab with a single click. The QR Code is displayed inline in a small popup.

Please note that this extension, unlike other extensions, does not require any special permissions (like access to your tabs and data). It is only loaded when you click on the button. So it does not have any unnecessary memory consumption and performance implications while not used.
Also note, that the QR code is generated completely offline. The URL of the Page you visited is not sent over the network (except when you click on "Edit QR Code" - that opens www.the-qrcode-generator.com). So it's probably as good as it gets regarding privacy  and security.