I’m putting these solutions here in case someone else is searching for the same problem.
1. I couldn’t send IMAP email using Outlook 2003. Uninstalled McAfee Spamkiller, and now it works just fine.
2. I couldn’t see .pdf files in Firefox after I bought the Adobe suite. Turns out, I had an old Acrobat Reader lurking around. Once I uninstalled that, I was able to view .pdfs again.