This adds-on will tell you how famous your blog/site is and every blog/site you visit. Simply install it on the lower right of your Firefox browser on statusbar. The status will change according to the current page in your browser. What i like most of this tool feature is the highlighting of nofollow links, it helps recognise efficiently which links is not in Dofollow.
An excerpt from HubSpot on how PageRank is calculated:
0-3: New sites or sites with very minimal links
4-5: Popular sites with a fair amount of inbound links
6: Very popular sites that have hundreds of links, many of them quality links
7-10: Usually media brands (NYTimes.com), big companies or A-list bloggers.
If you're just new on using Firefox, you can search lots of useful Firefox extensions available at the Firefox add-ons site, or simply on your firefox browser click tools> click add-ons and a pop-up window for add-ons option opens.