Linux single applications can be run also via browser, but by default they will be displayed in a virtual desktop, on a black background and some functions like resizing will be not possible.

To improve user's experience, it's possible to launch the custom application with its window manager:

Some examples for xterm:

GNOME
mutter & xterm 
KDE Plasma
kwin & xterm
LXDE/LXQT
openbox & xterm
Cinnamon
muffin & xterm
MATE
marco & xterm
XFCE
xfwm4 & xterm

If the application is Firefox, to avoid that it is started before than the window manager, use:

xfwm4 & sleep 1 && firefox