Most of the people bookmark their favorite websites and these bookmarked links must be backed up. You can backup Firefox bookmarks on Mac or PC, which you may transfer to another computer or restore when you install fresh OS.
Just launch Firefox, from the “Bookmarks” menu click on “Organize Bookmarks…” option
Now, click on “Import and Backup” > “Export HTML…” and save that file on your system and that’s all
You can also backup Firefox bookmarks using “Backup…” option instead of “Export HTML…”, this will backup the bookmarks as “.json” file. If you backup bookmarks as .json file then to restore it use “Restore” > “Choose a file” option.
see Firefox section for more Firefox tricks