Yes FF extensions are quite useful and can make life much much easier but they are just as dangerous or more so than an upatched IE, and they can also be a heck of lot more cumbersome than any version of IE. Take a few minutes and do a little research, avoid the "Firefox is more secure by default", and the "Firefox is faster than..." bandwagon, every "update" for firefox 2 with the exception of 2.0.0.9 has had at least one security fix.
http://www.mozilla.org/projects/security/known-vulnerabilities.html
FireFox 3.0 contains 300 fixes for memory leaks. 300, think the beta operates faster? I wonder why...
http://blog.mozilla.com/blog/2007/11/20/firefox-3-beta-1-ready-for-testing/
Everything I typed here can be found on the mozilla website, and much much more.
I wouldn't say one browser is better than the other because of security, bottom line, the net is a dangerous place, browse with caution. Or use a command line based text only browser... Not much fun in that though.
Use what you like, update it regularly, and stay away from questionable sites and hotlinking
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And just for the record, I use Firefox. I don't use a lot of extensions or themes, I just like some of the options better, like the download history, and bookmark organization. But its getting a bit frustrating to have restart every time an update is installed. Yes it takes me back to the pages I was viewing but its still getting to be a tad bit old...
Oh yeah, the movie was pretty good too, for the 80's