A really weird problem in Opera

I re-installed Ubuntu 8.04 on Margaret's Dell yesterday and found that Opera was behaving in a very strange manner.
What was happening was that nothing would open in Opera, even from it's own speeddial, but Firefox would open and display the page.
So, I posted to the Opera Linux forum and got a resolution.
The problem was that, for reasons I do not understand, file types htm (and similar) were set to open by Firefox. Setting this back to Opera immediately resolved my issue.
I have to say that I would have taken a very long time to figure this out on my own. TG for forums.
Anyway, now for the details:
Go to Tools>>Preferences>>Downloads and look for the line with extensions htm, html, shtml. Highlight it and click the Edit button.
Now, verify that this file type is set to open by Firefox. then click the radio button to Open with Opera and you'll be back to normal.