Logging me out of ICM on Firefox

Firefox randomly logs me out many times a day.
Can’t use the site anymore on my main browser.
Clearing cache and removing ICM cookies didn’t help.
Maybe it’s something to do with there being 2 sites with different login forms? I’ve tried logging in and out from both, but it makes little difference. I’ve even changed my password.
When I try to re-login on old site, it says something like form expired and sometimes the login still works. Then if I log out and log in again, it doesn’t form-expire.
On the new site’s login form, it will sometimes just do nothing when I try to login. Like just now I logged into discuss.icheckmovies.com from the 2nd attempt. Last time I gave up and went to login on the old site.

It’s all good on Chrome.

edit: Think I managed to sort it out somehow, maybe deleting cookies again helped.