View the page source. If the "a href" tag has rel=nofollow then it is no follow. If there is NOT a rel=nofollow then it is a do follow link.
Don't forget to check for the robots meta tag, if it contains nofollow then it has the same effect as nofollow attribute, a lot of webmasters get fooled this way.
In firefox you can right-click on the link and choose properties, it should say Relation: If its blank its do-follow, if it says nofollow, well no brainer. You can alos download SEO for firefox at seobook.com] and it will highlight all nofollow links in page with bright red.
I'd go with Search Status, it will show you Nofollow links and PR of web pages. so if you are not using G toolbar so search status can help for Green Bar Eric
You can also install SearchStatus extension for Firefox that enables you to highlight nofollow link on the page you're visiting.
I'm using firefox add on- searchstatus You can see the pink highlight if the link is nofollow, other than that, searchstatus show the alexa ranking and PR as well