old 32bit gtk2 app won't launch

It worked and works fine in openSUSE 42.3. I cloned 42.3, then online upgraded the clone to openSUSE 15.1 using zypper dup. The ancient 32bit gtk2 app is in /usr/local/ shared by both, so I know it still works. But, 15.1 won't launch it. If I try to launch it with gdb, it reports

Quote:

not in executable format: file format not recognized

Since it normally launches from a wrapper script, I tried the binary instead, with
this result:

Quote:

error while loading shared libraries: libxul.so: cannot open shared object file: No such file or directory

File libxul.so is in the same directory as the binary, so I changed to it first,
then tried to start, but get the same cannot open message. How can I get this old
app to run without switching back to 42.3?