I saved my breakpoints to a file, then in a new session,
"source"d the file to recreate them.
However, they weren't recreated, because I had neglected to
"set breakpoint pending on":

(gdb) source /tmp/B
Function "nsDOMWindowUtils::SendMouseEventCommon" not defined.
Make breakpoint pending on future shared library load? (y or [n]) [answered N; input not from terminal]
No source file named EventBinding.cpp.
Make breakpoint pending on future shared library load? (y or [n]) [answered N; input not from terminal]


One way around this would be to arrange for this to be handled explicitly in the
saved script.