Hi nogajun,

You rated 1 star. Please do not use this review as a support forum. If you need help use the official support at https://www.stefanvd.net/support.
I am happy to help you over there.

The Note Sidebar Firefox extension uses a plain text box field. There is also no character limit or block set for specific character sets, such as Chinese or Japanese. Additionally, on the Options page, you can change the plain text format to rich text.
Please check you are using the latest Firefox web browser, and the latest Note Sidebar browser extension.

If you have any further questions, please do not hesitate to contact me at https://www.stefanvd.net/support
I am happy to help you there.

Thanks,