I have not tried checking Norton's site but often some components of Norton's software needs updating after Firefox itself updates. Firefox tends to update at least every six weeks.

Please ensure your Norton software is all fully updated, hopefully it will then work again.

Run a Norton Live Update to get the latest version of that Firefox add-on; run it repeatedly, if necessary. We have had reports from some Norton users that it took 4 or 5 runs of the Norton Live Update procedure to get all of their Firefox add-ons updates.