I mean Yubikey rather than Ubikey.

I think this is a question for Yubico. According to https://www.yubico.com/yubikey-function-comparison/:

FIDO Universal 2nd Factor Authentication (U2F): An emerging standard from the FIDO Alliance for applying two-factor authentication to any number of web-based applications, such as Gmail. Works via the browser, Chrome today, Firefox under development, and does not require any drivers. Does not require any client software or drivers.

Feel free to ask them for more info.

Thanks for your post.

I think Yubico may be thinking that it is under development by Firefox. At https://www.yubico.com/why-yubico/for-individuals/dropbox-for-individuals/ they say:

Running Microsoft Internet Explorer or Mozilla Firefox?

Soon adding FIDO-based second-factor verification will be easier on these two platforms as Mozilla is currently building support for U2F and Microsoft is working within the FIDO Alliance to eventually bring support to Windows 10. But for now, there are some additional technical steps to take for Yubikey two-factor authentication if your browser isn’t Google Chrome.

hi, you could see if https://addons.mozilla.org/firefox/addon/u2f-support-add-on/ helps in your situation.

Thanks for that. I have installed the addon, but do not expect it to help with gmail, since I have read that Google do not yet allow gmail 2fa to work with Firefox. I have yet to try it with anything else. I could try Dropbox, but it is going to stop running on xp in about 10 days time, so there seems little point at present. Nevertheless, it may be useful with other sites in due course.