I have that feature where middle-clicking (MB2?) opens a floating icon for scrolling up and down by moving the mouse up and down enabled in Firefox. about:preferences -> Browsing -> Use autoscrolling Eitherway, it appears somewhere the information that the ctwm titlebar has a certain height is lost or ignored, and the scroller-icon is created 20-30 pixels above where the cursor was when MB2 was pressed, causing the Firefox page to start scrolling downwards immediately (instead of the cursor defaulting to the neutral position in the middle of the up-down icon). Turning off titlebars for Firefox causes it to appear in the expected position, but I have no idea if it is Firefox misbehaving or something else.
On the topic of gtk applications I also have an issue with thunar-1.8.2 on gtk-3.24.1, where in the sidebar that contains shortcuts to e.g "~/Documents/" and "~/Desktop/", hovering one of the items causes the cursor to start blinking rapidly between the "standard" pointer-cursor and the X-shaped cursor that usually appears when the cursor is over the background of ctwm, I guess because (whatever gtk calls it) the tooltip that appears in a textbox does something unexpected with the focus For what it is worth I have both of these issues in twm-1.0.10 as well, so there is that.
