Hi, no it is not necessary It uses Ask.com but you do get the green tick marks back for safe sites.

Norton Safe Web is good and if you use a password manager Identity safe is good. But good only goes so far them all. Always :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Please let us know if this solved your issue or if need further assistance.

Firefox does not protect you explicitly from phishing but does for malware which are in the list Firefox uses that is from Google.

If the site is a risk, Firefox will popup a red page from Google warning you.

Norton uses the list also but also uses it's own information which is crowd sourced for when people submit info or virus for samples as well as scans.

As Firefox is not a specialized anti-virus or anti-malware program using Norton Safe web is a good idea.

This article describes protection against loading phishing sites and known malware distribution sites: How does built-in Phishing and Malware Protection work? As you will read, it kicks in once you request the page; Firefox's doesn't pre-mark search results with a safety rating.