そんなにたくさんは使ってないですがこんな感じ。
Pluginのほうは、Flash含めてとりあえず問題なく動作している模様。
Norton IPS については、サポートフォーラムに記事がありました。
http://community.norton.com/norton/board/message?board.id=nis_feedback&thread.id=59221
>Re: Norton Toolbar Support for Firefox 3.5
>
>As promised, we have an update for you. We have an ETA for the Firefox 3.5 hotfix!
>The hotfix will be available for download on 7/15.
>We have been working with Mozilla closely and testing our fixes with each and
>every public release of Firefox 3.5. We believe that we have fixed all issues now and
>are working on a hotfix that you can apply to your Norton Internet Security 2009 and
>Norton 360 v3 products in order to get FF 3.5 support.
>You do not need to wait for our 2010 products, or pay for anything.
>
>Also, our 2010 beta just released today, fresh from our labs and it does support Firefox 3.5!
>Check it out at: http://www.symantec.com/norton/beta/
ということで、7/15頃にFirefox3.5に対応するHotFixを出すと言っています。
それから、現在公開中の NIS 2010 betaはFirefox3.5に対応しているとも言ってますね。