We developed a Firefox add-on to use with thagg.com. It is very easy to use.
Step 1) install it, click here
Step 2) restart Firefox
Step 3) visit a random page
Step 4) select some (formatted) text
Step 5) right click on the selected text, select 'thagg this'
Use the toolbar button to tag a link/page.
Thagg.com will be opened in a new window. After you are signed in, you can save your selection.