Copying Bookmarks—for Intermediate skilled user

I transport a portable hard-drive between my office and home. I was using Firefox on my computers at work and home even before I knew about Portable Firefox. Now that I've installed Portable Firefox on my portable hard-drive, I'd like to copy the many bookmarks I have accumulated in Firefox so that I have access to them from the portable hard-drive. For those times I leave the portable drive behind, I also want to have access to my bookmarks from either desktop computer. Is there a simple method for copying booksmarks from Firefox to Portable Firefox and vice versa?