I have Windows XP SP2 and Firefox. A recent problem with email in Outlook Express is that I cannot access web links. Don Curtis
The Microsoft Knowledge Base has a help article on this: Internet shortcuts in Outlook Express do not start Web browser. Since Outlook Express is a companion program to Internet Explorer and both are Microsoft products, the suggested fixes include making IE your default browser and, if necessary, correcting the HTML file associations to point to iexplore.exe (ie IE). If you can get web links working for a bit, you can change the default browser back to Firefox and hope that Firefox sets itself up correctly.
Another possibility is that a popup blocker is preventing the links from working.
Either way, bear in mind that phishing exploits and other attempts to install malware can start when you click an obfuscated email link, so it could be a security risk. It's safer to copy and paste links as plain text.
Also, Outlook Express has been superseded by Windows Live Mail. I'd upgrade to that before trying to fix Outlook Express.