If you are on Windows, a microsoft or IE update may reset your defaults. Go to the start menu, left click, select "set program access and defaults" by left-clicking; this will bring up the add or remove programs window. For some reason, I have 2 of these icons in my start menu, and one doesn't work at all. I think a duplicate icon or plug-in is being used for each browser. Select "custom", the last optiion, and then click on the double downward arrows. The first choice given under the various headings is to choose a web browser. Unclick "use my current web browser" and go down to the bottom to click on Mozilla. I have found that various legitimate websites also reset your browser because they use IE or something else. It's a real pain.
There was a similar query posted a week or so ago, and someone more expert than me made suggestions; you might check that out.
Good luck, and happy winter occasions!
UPDATE: The topic was Outlook Express, and how to disable/remove it. Same techniques are used. Here is the link to the BC thread:http://www.bleepingcomputer.com/forums/t/184807/how-to-disable-microsoft-outlook-in-service-pack-3/
Edited by fuzzywuzzy6, 25 December 2008 - 07:44 PM.