Try this:

Export from Opera File > Import & Export >> Export as HTML

Then Import into Firefox Bookmarks > Organize Bookmarks -> Import & Backup - Import HTML... = from an HTML file

It doesn't work. I've tried both the File/Import/Opera but the selection window in blank; and the Manage Bookmarks/Import way but nothing imports.

Does anybody know how to do this?????

It doesn't work. I've tried both the File/Import/Opera but the selection window in blank; and the Manage Bookmarks/Import way but nothing imports.

Does anybody know how to do this?????

Yes it does work. In OPera one needs to use Menu/settings/Import & export/export bookmarks as HTML and NOT the export found in manage bookmarks.

For the tabs I had both OPera & FF open and manually (right click) copy address and paste into FF with new tab using the brilliant Tree Style Tab add-in.

The posted instruction for importing bookmarks, cookies, and passwords does NOT work. Exporting as HTML from opera and the importing the bookmarks into Firefox works for bookmarks but nothing else. plus the imported bookmarks needs to be sorted since firefox messes up any structure to the bookmarks.

double post deleted

To Mr EdMeister and others.. Tried your instruction but there was a missing step for mozilla 4.0. There is no "organize bookmarks" in my 4.0 Instead I find the following sequence: "bookmarks>Show All Bookmarks>Import and Backup>Import HTML>from an html file". For some wierd reason "organize" has been renamed "show all bookmarks" which is a dialog for managing bookmarks. And speaking of which, that dialog refuses to save the alphabetized sort or probably any other sort type back into the bookmarks menu.. You must manually drag and drop the bookmarks into the order you want for a persistent presentation

Yep, that happens when you use information from an 8 month old thread, that was started by a user who was using Firefox 3.6.8 and not Firefox 4.0.

There were 2 reasons that Organize Bookmarks was renamed to Show All Bookmarks.
1. To match the Show All History menu item elsewhere in the interface.
2. Because the Library window doesn't really provide a permanent reorganization of a users bookmarks, when using Views > Sort > Sort A>Z Sort Order. That "sort" is temporary for only as long as the Library window is open.