Is there a way I am missing to resize the text of the forum? The tread titles are now huge on El Capitan unless I reduce the window size to half on the Macbook.
Not that I know of, Karl.
The thread-title font size was increased 'cause a bunch of Kemperites complained that they couldn't read it easily. Instead of bumping it up a bit at a time, it underwent one huge jump in size, which was shocking at first and took a while to get used to, but there've been no more complaints about reading difficulty.
Of course, you could use Safari's "Page Zoom" preferences window to set the forum to be 85, 75 or 50% of the standard size, but you'd have to endure smaller text overall.