Important information for Firefox 50
Due to changes in the Firefox 50, signTextJS add-on, that is used for signing in web sites do not work with this version.
The solution for this problem is to remove signTextJS and install The solution to this problem is to uninstall signTextJS and install new add-on, that provides the same functionality - signTextJS plus.
Another solution is to use corporate version of Firefox. There is fewer braking changes in this version and signTextJS still works correctly. Both versions offers same level of support from Mozilla and are updated simultaneously when security bugs are found.