I'm trying to integrate U2F Authentication in GWT project and I need to know if is this solution compatible with all new web browsers (Firefox, Internet Explorer, Safari...)? Normally in Google Chrome I've to install a plugin that's called "FIDO U2F (Universal 2nd Factor) extension". Is the same for others browsers?
Is there any way to work without a plugin for new web browser?
You had to install a plugin in Chrome in the past, currently (I think starting from version 40), this is not required anymore: U2F capability is built in from that version on in Chrome. As to which other browsers support U2F: currently none. Firefox supports U2F via the U2F Support Add-on, and is working on supporting U2F natively.
Microsoft reportedly will include FIDO support in Windows 10. It might be possible that browsers will rely on the OS-U2F-check then, and do not (need to) include FIDO support directly anymore. However, this is speculation only for the moment.
An easy compatibility check I'd like to carry out is to use the Yubikey's demo site.. It will be reported immediately when your browser does not support U2F (try opening the demosite in Firefox and see what happens).