Bottom right of the browser, there's a little magnifying glass thing. Left-clicking on that will bring up the site settings, and in that window there's a button for Global Settings.
Excellent, thank you!
It's a bit harder to see quote boxes, but I'll manage. I'm getting thrown by the change of clicking on a link changing the page instead of making a new tab. But, I read earlier that the middle mouse button will do exactly that in FF...
Still, this may be a fix for me, but it has its flaws and doesn't negate the problems (visually, and functionally) with the new forums.
It's also harder to tell which topics have gotten new replies - the black and grey folders don't stand out at all against the background.