To all those who posted replies to my question as to whether or not I could safely delete three files, the answer from SebR did the trick. I went to Firefox extensions, deleted the Evernote webclipper file and hey presto, no more advice window from Norton when I start my browser. Thanks guys.
I have no use for Evernote so have deleted it. However, whenever I open my browser a small window with "evernote_native.bin is safe" appears. Norton has identified the location but I see that there are two other Evernote files in the same location. These files are "evernote_usage_metrics" and "evernote_webclipper.sqlite". Can I safely delete these three files? The location on my laptop is "(my name)\AppData\Roaming\Mozilla\Firefox\Profiles\wuqc0b0t.default" Thank you for your help.