SplitFrame is a bookmarklet I wrote for work to compare two different instances of a site. Usually, I’ll use it to compare my development instance against deployed. SplitFrame’s main selling point is that as the left frame is navigated, the right will follow.

It proves useful pretty regularly for me. Let me know if it does for you too. Suggestions/forks welcome.

Link: http://rocktronica.github.com/splitframe
Source https://github.com/rocktronica/splitframe