I don't know what you mean by saying 'bookmark keyword', but to paste into the location bar, you just need to use the hotkey 'Ctrl+L' to select the location bar, then send keystrokes.
Sorry I didn't make it clearer.
You can assign your bookmarks keywords in the Firefox "Bookmark Properties" dialog.
Then you can type the keyword into the location bar to launch the bookmark.
Works about the same as the keyword search function.