Firefox not remembering settings

Question

I have this problem since recently (I have installed extension LiveHTTPHeaders), my firefox settings are getting lost everytime i restart it. I have set it to open tabs from last time, to load tabs only when they become active, to use google as search engine. And there i go restarting the browser and having my search engine changed, the tabs it opens show the websites of all my addons, loading all of them, I don't know what this is. Besides, I get a message now and then saying an application is trying to change my default search engine. Now is there a way to find out what application is doing this? Thanxxx...