For the past couple of weeks I find that I’m having to continually log-in whenever I try to do anything in the Eve forum - e.g whenever I open a thread in a new window, try to add a Like, try to make a Reply etc. If I Open New Topics in a new tab it tells me the page doesn’t exist or is private, but I can open it in the current tab OK. I’m using Firefox 66.0.3. I don’t see this behaviour on any other forum, and I haven’t changed any settings recently.
Could be I suppose, not sure when it was last updated - the ‘History’ tab only shows a Kernel update, not the list of all updates I expected to see. I think I perhaps need to de-install and re-install Firefox. Not sure why it would only affect Eve forums though, everything else seems to be working OK.
You might want to try Chromium. I believe Mint has it as a package. It’s basically the open source browser that Google base Chrome on - because they add their Google binaries into it.
I use Chromium on Debian Stretch (Buster is on my “to do” list) - Forums work perfectly well with it for me.