this is a very basic extension for Chrome.  It appends some text to end to the active tab's URL:  &emi=ATVPDKIKX0DER   This is the ID for Amazon US.  

For outside the US, you need to look up your country's Amazon MarketplaceID.  At time of writing, one list is at https://docs.developer.amazonservices.com/en_UK/dev_guide/DG_Endpoints.html  Then you can edit backgound.js and replace the text on line 3.

After clickingf the button, if it's an Amazon search, the results will be for products shipped and sold by Amazon only.  For years, we were able to do this on the left hand filter.  Recently, the option seems gone.

To install, download the "URL APPENDER" zip file, go to extension manager in Chrome and enable developer mode, and then load this extension by clicking "Load unpacked".