A relatively complete protection

I use Norton Internet Security on three professional positions for several years. I use a lot browsing (Firefox) and email (Thunderbird). I never had a problem and found that its warnings are relevant. No sensitive penalty on computer performance. It is financially more interesting to buy a new version every year taking advantage of promotions (like Amazon) and install it in place of the previous one rather than renew the subscription for Norton link. One complaint: I would like the antispam function also supports Mozilla Thunderbird (antivirus function works correctly with Thunderbird).