Seems to be a day of coincidences. From my bookmarks I clicked on the following link for Tech News in Asia, which I discovered on Anandtech. I've visited the site before, but this time I noticed a green icon with a plus mark in my Firefox Search window. Clicking on the Search icon, I saw two new search engines associated with this site, but I could not see my default and optional search engines, except by clicking a link. The change was not permanent. When I used my back button, my default and optional search engines returned.
http://techcrunch.com/asia/
So my questions are... can I prevent this or worse changes using embedded Firefox features? Is there an add-on that can effectively do the job?