I had a quick look at the source. At least the main abiword has three methods for opening urls, decided on compile-time and of course 100% undocumented..
If gnome is available, use a function in libgnome. If gtk >= 2.14, use gtk's open_uri. Else try from a list of FOSS browsers.
What sucks in this combo, and is pretty much undocumented, is that gtk's open_uri doesn't do zat without gvfs. I'm not sure if this is a compile-time dependency of gtk, or if it would be enough to install gvfs.tcz runtime.
Looks like I'll have to modify it for the next build, to force it to use the list and add opera there.
edit: well, it works without gvfs if firefox is installed. I see, it's because the gtk uri code was not there yet in 2.6.8.
For reference, here's the list it tries:
static char const * const browsers[] = {
"sensible-browser", /* debian */
"epiphany", /* primary gnome */
"galeon", /* secondary gnome */
"encompass",
"firefox",
"mozilla-firebird",
"mozilla",
"netscape",
"konqueror",
"xterm -e w3m",
"xterm -e lynx",
"xterm -e links"
};
So for a quick fix, symlink sensible-browser to opera.