I recently upgraded my computer and therefore had to go through the pain of installing the whole operating system and all my favorite applications from scratch. Luckily they're not that many and some of them make the process of moving to a new PC a lot easier these days.
I'm talking particularly about Firefox, which features an embedded tool to backup bookmarks and import them back to your newly installed Firefox anywhere else. To use it, just go to Bookmarks > Organize Bookmarks and once you're in the Bookmark Manager, go to File > Export. Firefox will save all your bookmarks as an HTML file which you can import later in exactly the same place.
Also, for those of you who make use of the Firefox built-in password manager, you may also want to backup your passwords. While Firefox doesn't feature an special embedded tool for that like it does for bookmarks, you can use this handy extension. Password Exporter lets you backup all saved passwords to a CSV or XML file and import them in another computer.
Finally, if you'd like to make a copy of your whole user profile in Firefox, I definitely recommend using MozBackup. This excellent tool will backup your whole profile including bookmarks, browsing history, cookies, passwords and cache. I used it to move all my data from the old PC to the new one and it worked perfectly well.