After getting the “known” firefox error message that my move could not be sent I reloaded my tab as usual. When this did not help I killed firefox and restarted it as usual. As this did not seem to help (just the loading circle thingy), I installed a java update (apple computer, firefox browser, 8u60 jre update) which was a bad mistake.
I tried deleting my cookies, trying chrome and safari in vain, checking my java security settings, even the peerconnection thing because google showed it. I did not even get the loading circle thing, I could not connect at all.
Finally, I deleted my java installation and installed 8u40 jre update. After that, things have been working fine (but it took me an hour for all this).
So, I would like you to check into problems with this newest java update. Also, it is very inconvenient that without java one has no way to contact the other player or the mods here (as far as I can tell).
Summary:
Mac, OSX 10.7.5
Firefox 40.0.3
Java jre-8u60
-> No connection to ogs possible with any browser.