I use the bookmark manager that is built-in to Firefox. I also use a browser extension that checks for dead bookmarks and redirects in order to update them for me.

I try to keep them organized and tidy in a hierarchy. I bookmark any website I find useful so I don't have to use search engines unnecessarily and most of my websites autocomplete within a few keystrokes.

In summary, I am happy with the bookmark manager. In the future I would like to switch to a plaintext format, perhaps like org-mode if I can get it integrated with the browser. The reason I want this is so I can put that file up on my website to share with others.