Preferred Applications should also modify gvfs-open/gio. Web Browser of Settings->Preferred Applications impacts xdg-open/exo but not gvfs-open/gio. The latter (gvfs-open/gio) is used by Evolution, HexChat, and a long list of other applications. Its active settings: gio mime x-scheme-handler/http gio mime x-scheme-handler/https Changing its settings: gio mime x-scheme-handler/http <BROWSER> gio mime x-scheme-handler/https <BROWSER> Where <BROWSER> is, for example: firefox.desktop google-chrome.desktop
*** Bug 10977 has been marked as a duplicate of this bug. ***
Sean Davis referenced this bugreport in commit 8bc59ad1c48df132e917337bd08211be58af5bb1 Configure gio mime defaults with exo-helper (bug #14633) https://git.xfce.org/xfce/exo/commit?id=8bc59ad1c48df132e917337bd08211be58af5bb1
The above commit adds support for this. Can you please test and confirm it works as expected?