Click on Firefox..at the very top to the Left..then a drop-down list will appear..at the top of the 2nd column to the right in the list you will see 'Bookmarks'..put your mouse arrow over it and your bookmark list will show including the option to bookmark the page you are viewing. As before right clicking on any in the list can give you the option to delete an entry.

I was assuming your question was regarding Firefox 4...then I noticed your system details show Firefox 3.6.15 ? My answer was for the new Firefox 4 Beta release.

See:

• Use bookmark folders to organize your bookmarks