hi
offtopic, isn't it?

use Bookmark Synchronizer (Mozilla/Firefox Plugin)
https://addons.mozilla.org/extensions/moreinfo.php?id=14&vid=15&category=Bookmarks

greets
christoph

Your question has nothing to do with Java, but I will tackle it
anyway.

Oddly browsers have import commands (You need to dig around in the
menus to find them.) without the corresponding exports.  So, for
example, you might go into Opera and click import and hope it offers
an option to pick up Firefox bookmarks.

This of course presumes both browsers are running on the same machine.

To export to a different machine, you have to find the files where the
bookmarks are hidden, copy them to CD, and copy them back to the same
names, in the same version of Firefox on another machine.

How do you find such files?  You can use the filefind feature of
windows telling it to look for a file with the text from one of your
favourites inside.  When copying them back, make sure they are not
marked read-only.  If so, use attrib /R *.* to undo that.

Or you can use your intuition digging about the file structure to
discover that Firefox hides the bookmarks and all the other
configuring stuff in:

c:\documents and settings\administrator.roedy\application
data\mozilla\firefox\profiles\gt4rcgpi.default]

That is where they are on my machine; yours will be slightly
different.

When copying such files, make sure Firefox is not running and you have
a backup.

The difficulty of moving apps from machine to machine is deliberate
originally to make like awkward for pirates, but also mindlessly
perpetrated in free software.