Increments the last number in the URL of the current page. This is useful when visiting a row of numbered pages. The plus icon only shows up for relevant pages.
Say you're reading blog post: http://www.osnews.com/story/222/
By clicking on the plus you go to page: http://www.osnews.com/story/223/
It also respects any adresses with zero padded numbers. Say you're reading the page: http://www.us-cert.gov/cas/tips/ST04-009.html
By clicking on the plus you go to page: http://www.us-cert.gov/cas/tips/ST04-010.html
You may use the keyboard shortcut Ctrl-Alt-Right instead of clicking the plus and Ctrl-Alt-Left to decrease the number.
In the options page it's possible to change the regexp of the number that is incremented. By changing it to "\d+" the first number instead of the last is incremented. It's also possible to set the number of steps that the number is incremented.