matthewdb said:
I am going to the main page:
https://www.physicsforums.com/
It will work for a while if I clear the cache and then it will quit on my next visit. I've just started using private mode and then it works fine. Private mode doesn't allow websites you are browsing to see your cookies so I'm sure it's a cookie problem with PF.
Actually, private browsing in Firefox does not change your cookie policy at all. It allows sites to do whatever is allowed by your normal cookie policy (including any exceptions you've set up); this also applied to the infamous flash cookies. Instead, what it ensures is that all cookies (including flash cookies) materialized during the session are deleted on termination. (Of course, it also deletes history and cache used in the session as well).
Given that this solves your problem you might want to try setting a cookie exception for physics forums that keeps cookies only for the session (downside - you will have to log in every time).
Personally, I disable cookies by default for all sites, and allow them only for sites that I want. This gets rid of all advertising cookies from associated advertising sites. I also completely disable flash cookies and refuse to use sites that require them (this you can't do from firefox; googling should get you instructions for this, if desired).
However, in your case you might say it is too late for this approach because you have too many cookies remembering logins that you don't want to lose.
Pick your poison.
[Edit: I realize that even before I became a paid member I never got ads because of security addons I have in firefox; not primarily adblockers (though those exist), but many ads are eliminated due to security policies). So if your problem is ad related, I never had it. I would not want to recommend ad blockers. Instead, I encourage contributing to this site.]