The default double-click time (the maximum interval between two mouseclicks for them to be recognized as a double-click) is (imho) too short: 250 ms. Increasing the default to 350 ms would prevent a lot of frustration. For elderly people in particular, and for beginners who don't know how to change the setting. Default settings should be reasonable, and 350 ms seems a more reasonable default to me.
Xfconf seems a more likely component for this bug report. I'm not sure though, so please correct it if it's the wrong choice....
Sorry. It should be xfce4-settings, I think.
Gtk's default is 250ms.
I don't think it's a bad idea for the desktop environment to adjust the toolkit's hard-coded defaults to ensure a proper user-experience. The default parameter in GTK+'s GParamSpec is likely more arbitrary than anything. In 2001 it went from 1 to 1000, and shortly after it went to 250 without any explanation what was wrong with 1000. I think KDE's equivalent default is 400ms as comparison. I'm curious what GNOME-shell sets it to (if not using the hard-coded default), although not curious enough to install it or dig through reams of JS code to find out :) I must always adjust this to a sane value when installing XFCE anew (currently have it set to 800ms without any ill-effects). If you google for "gtk-double-click-time" you can see all of the trouble this poorly chosen default value has caused for users of distros that don't provide a sane value over the years.
Looks like GNOME uses 400ms as well: https://git.gnome.org/browse/gnome-settings-daemon/tree/data/org.gnome.settings-daemon.peripherals.gschema.xml.in.in#n130
Set to 400ms in 8f95e08.