DashBlog is a Tumblr-style Firefox extension that makes it easy for you to share screenshots of web pages on any blog or on Twitter.
You open a website in Firefox and select “Grab a screenshot” from the contextual menu. DashBlog will bring up some annotation tools in the sidebar.
Pick the crop tool, select an area you want to capture and add annotation using the Pen Tool or add some arrows and text. When you are done, click the Post button.
With DashBlog, you can publish screenshots on blogs that are hosted on Tumblr, WordPress, Blogger or even Twitter. Alternatively, you may also save the screenshot to your local desktop.
Get DashBlog from Firefox Add-Ons website.
Related: How to Capture Web Page Screenshots