AliZon for Chrome
More About AliZon
It is very simple: just install this extension and while you browse some product from one of these two stores, it will automatically look for the same product is available in the other. If so it will show you the link to it.
If it doesn't find the same exact product, it will suggest a link to the most relevant search. This way you can easily compare between the two stores, which surely will help you to save some money
If you found this extension useful, please give it a good review. :)