Norton Toolbar is always incompatible with the new version of Firefox. Case in point: toolbar 2015.5.4.10 is only compatible with Firefox 40.0.3, and there is no new version available on Norton Update .Mozilla came out with 41.0.1 last week, and 41.0.3 today. And next week version 42 will be issued! After talking to as many Mozilla people as would talk to me, I have learned this..Norton Toolbar will show incompatible with new version EVEN IF IT STILL WORKS!! Why can't the toolbar be left operational and only disabled by the user if found to be incompatible? I'm sure Norton and Mozilla can work this out.
I have been forced to disable Firefox auto updates and use Firefox 40.0.3, which luckily was still available on line.
A second suggestion would be for Norton to place, in the description of Norton Toolbar, which version or versions of Firefox ARE compatible with that version of toolbar.