I just had the same hard denial from Safari and it went through successfully with Firefox. So... nevermind.
It's just the crappy new forum downgrade.
I'm not certain about this, but I just tried posting something twice from Firefox and it failed HARD twice. It was the whole Page Not Found error that just refuses to take the submit.
I hit the back button, copied my text, opened Safari and pasted my reply into the window there and hit submit and it went through, no problem.
This is not to say I haven't had issues from both browsers with this forum and it might have just been one of those "moments" where our wonderful new forum upgrade bit me in the ****, but I'm starting to raise an eyebrow. Maybe two.