If you have multiple tabs open at once, you can bookmark them all in one go. For this Choose Bookmarks Bookmark All Tabs (Ctrl+Shift+D). You will get a dialog box as shown below asking you to name the folder for the bookmarks.

To reopen that set of bookmarks as tabs, drill down through the Bookmarks menu and submenus to the folder you want to see and then choose the bottom menu item (the one labeled Open in Tabs).

It’s also possible to start up Firefox so that multiple tabs are displayed. This functionality is not available in bookmarks. Use a URL in this format to make it happen:

http://www.example.com/page1.html|http://www.example.com/page2.html

The vertical bar character (|) separates the URLs for each tab. This syntax can be used on the command line when starting Firefox, or it can be specified as the default home page in the ToolsOptionsGeneral dialog box. Because the pipe character has other historic uses, this syntax is not locked in stone yet, but it is available and working in Firefox 1.0.