Not likelly a Firefox issue. Have you pressed the NumLock key?

Reboot the computer?

Separate Issue; Your System Details shows;

Installed Plug-ins

Adobe PDF Plug-In For Firefox and Netscape 11.0.9 Adobe PDF Plug-In For Firefox and Netscape 11.0.11

Shockwave Flash 18.0 r0 Shockwave Flash 16.0 r0 Shockwave Flash 15.0 r0
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Flash: Grab the uninstaller from here: Uninstall Flash Player | Windows Uninstall Flash Player | Mac

Then reinstall the latest version.

Flash Player Version 18.0.0.203
https://www.adobe.com/products/flashplayer/distribution3.html Note: Windows users must download the “Internet Explorer” and “Plugin-based browsers” installers.

Thanks Fredmcd I am using an apple keyboard and it does not have numlock key ! and have just rebooted ! Anton

Skip==

antongoodrick said

I am using an apple keyboard and it does not have numlock key !

and have just rebooted !

Skip this too

also see http://osxdaily.com/2014/12/01/number-keys-not-working-mac-keyboard-fix/