We maintain many docs in html format on a local shared drive. I wanted to launch my html editor of choice from within Firefox. I found the extension Launchy that does what I want.
Unfortunately, it didn't find Komposer, the bug-fix release of Nvu, automatically. I had to generate a launchy.xml file as explained on the main page.
I also learned that the 'command' entry should not contain double quotes! Otherwise Launchy ignores the entry.