Over the course of some days i have installed and uninstalled Firefox version 21, version 3.5, and version 2.? The problem was a constant and seemingly never ending stream of popups, whining that the site I wanted to visit had a non-acceptable security certificate, and that I would have to add an exception to be allowed to go there....but it would take four or more clicks to satisfy Firefox. Then while on that site I would click on a link, and the popup scenario would be repeated. Site after site. Again and again. I looked online for how to disable it, and nothing suggested worked, or worked for very long. I tore into 'about:config' and changed 'true' to 'false' everything I could find relating to security certificates. Nothing worked or worked for very long (Firefox seems to have some sort of protection mechanism to undo user changes). As last resort I rolled back from version 21 to 3.5 to 2.something. Finally I ditched Firefox in disgust. If anyone has a solution to this, I'd like to hear it, and if it seems feasible, I may give Firefox one last chance.