I tested with FF3.6 and FF41. Same behaviour.
The problem (apart from the nuisance of repeated logins) is that you lose any typed forum messages (typing a forum message is apparently considered "inactivity", from a technical point of view, lol ).
For example, I logged in just before typing this message, and now (I guess 10-15 minutes later) I wanted to submit it, but it was discarded and I was asked to log in instead. (My impression is that in the forum section, i.e. when submitting a message, it happens much more often than elsewhere on criticker, where I am logged out more rarely, I think. But my impression might be wrong.)
Getting logged out automatically on criticker happens to me quite often and just happened again today, when I wrote a lengthy reply to a film review ... it's all gone too and I don't have the energy to write it down all over again. Assuming this happens to others as well, I guess it would be a good idea to avoid frustration for criticker users by
- 1) either extending the inactivity logout time (I think anything more frequent than once a day is really overkill)
- 2) or adding a checkbox next to the login button allowing for a voluntary 30-day login (like wikipedia etc.)
- 3) or catching the submitted forum message so that after the login the message is submitted rather than discarded[!]
Of course implementing all 3 measures would be best.
If implementing only 1 measure, the last one would be the most helpful one, because in cases where the logout problem occurs not on your side but on the user side (corporate network, browser crashes, cookie issues, cashing issues, etc.), catching the submitted forum message of a currently-not-logged-in user is the only 1 of the 3 that would prevent the message from getting lost.
I hope this report is helpful.