Myth - "Firefox has lower System Requirements than Internet Explorer"
Reality - Internet Explorer 6.x has much lower minimum System Requirements than Firefox 1.x.
Myth - "Firefox is the Fastest Web Browser"
Reality - Opera (now 100% free) is the fastest Graphical Web Browser in Windows.
Myth - "Firefox is Faster than Internet Explorer"
Reality - Internet Explorer 6.x is clearly faster than Firefox 1.x overall and is significantly faster from a cold start. The argument that components of Internet Explorer may load during Windows Startup is nullified by Opera's start times.
Myth - "Firefox is Secure"
Reality - Firefox is anything but Secure with multiple unpatched vulnerabilities allowing exposure of sensitive data to local users. You only need one vulnerability to be insecure. Since Firefox was released users have been exposed to 26 security vulnerabilities and counting. 6 of which were market as Highly Critical.
"In the excitement that surrounded its launch last year, Firefox was unreasonably portrayed by some as having unbreakable security, but the vulnerabilities that have been detected in recent months are injecting a dose of reality into this myth, analysts say."
Myth - "Firefox is a Solution to Spyware"
Reality - This is very misleading and can lull users into a false sense of security. Use Secure XP to properly secure your system and get a REAL solution to Spyware. Firefox is nothing more than a Web Browser. Installing Firefox does not clean your system of existing Spyware infections or prevent you from manually installing anything in the future, including Spyware. These can come from Downloads, Email Attachments, File Sharing and by other means. You can still easily get infected with Spyware using Firefox as this exploit demonstrates.
Myth - "Firefox Blocks all Popups"
Reality - Firefox does not Block all Popups. PopupTest shows the "Drop down Popup" and the "Sticky Popup" are not blocked. Other types of Popups continue to get through.
More and sources cited here:
http://mywebpages.comcast.net/SupportCD/FirefoxMyths.html