To get ViewMarks to install, you will need to modify the xpi as described at Extensions. You will need to both add an entry to its install.rdf and delete several META-INF files. Once installed, add the following command to your rc to load it up:

interactive("viewmarks",
    "Open ViewMarks window.",
    function (I) {
        make_chrome_window('chrome://viewmarks/content/viewmark.xul');
    });

Basic bookmark management works fine, but features that obviously depend on Firefox chrome, like "open in new tab" won't work.