Java script in Blogging

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I'm grateful to Fundu Bytes for all his tips.
Here some problems I've got trying to implement them:
1.This script couldn't be pasted in the template editor without changing quotes and works in posts but still gives msie error:

p script type="text/javascript">if (navigator.userAgent.indexOf('MSIE')!=-1) document.write('Still using Internet Explorer!!!')a href=a href="http://www.mozilla.com/">Use Firefox !!! script type="text/javascript"if (navigator.userAgent.indexOf('Firefox')==-1)
document.write('This site is best viewed in Firefox.')script p>"