Here's an interesting bug related to the change to the (amazingly-narrow) fixed-width format:
Look at my message number 68 in the comments there. It includes a relatively-short URL linking to a forum thread. Depending on your choice of font size, the URL is longer than the tiny narrow window allotted for comment text. The margins for the text in that post are stretched to the width of the URL, but the margins for the skinny window are not changed, so a chunk of the text is invisible, like it ran off the right edge of the tiny ribbon of the comment "page".
You can see the same thing happening in Axeman's comment #93.
The text column available for my comment is a puny 430 pixels wide. I haven't owned a computer screen that narrow since 1990.
i7-4770K, H70, Gryphon Z87, 16 GiB, R9-290, SSD, 2 HD, Blu-ray, SB ZX, TJ08-E, SS-660XP², 3007WFP+2001FP, RK-9000BR, MX518