tedster - 7:22 am on Feb 21, 2013 (gmt 0)
Here's the main point - any browser plug-in also gets the PR number they show from Google servers. There is only one such number, and only Google itself actually calculates PageRank. Then it gets "passed around".
Here's a thread that might help you: Google PR - PageRank FAQs [webmasterworld.com]