Yeah, that's what I was doing as well: using tabs as a poor man's bookmark management tool, because Firefox on its own doesn't care about you actually using bookmarks to any real degree. I basically never had many of those 400+ tabs actually loaded.
Just in case you might want something different, you might like linkhut for trying to deal with this instead. It's something I've recently started heavily using myself along with the extension linkput making it extremely convenient to bookmark all the things. It's open source, bookmarks can be imported and exported via a single HTML file via the web or through various means on the command line (or other external tools) through its 1:1 Pinboard API. Along with other people using the flagship instance of it, it also turns into a great search tool in general, not only for just your own bookmarks. Also has RSS feeds for any combination of tags and user profiles. It's sick as hell.