Keep getting logged out of forum in Firefox

As per thread title. I select "keep me logged in" and when I open Firefox the next day, I find myself logged out again.

This doesn't happen if I log in to Opera (Chromium version)

Somewhat frustrating, as Firefox is my primary browser. Is this happening to anyone else?
Player since closed beta 2012. Full system specs: https://pastebin.com/c4rvbvSR
'Tongueslurp the Unspeakable' - skeleton archer in Fellshrine Merciless
Check your cookie settings (options -> privacy -> cookies)

Guess you're blocking the website.
Alright on pathofexile.com I've got several cookies. The two that stand out are:

session_start - expires: at end of session
PHPSESSID - expires: March 23 2015

How do you change this? I don't want them to expire. They must last until the year 2099 if it comes to that.
Player since closed beta 2012. Full system specs: https://pastebin.com/c4rvbvSR
'Tongueslurp the Unspeakable' - skeleton archer in Fellshrine Merciless
Still no dice
Player since closed beta 2012. Full system specs: https://pastebin.com/c4rvbvSR
'Tongueslurp the Unspeakable' - skeleton archer in Fellshrine Merciless

Report Forum Post

Report Account:

Report Type

Additional Info