When I do a major revamp of a site I regularly take a screenshot of what it was originally and then what I’ve changed it to.

When I was on OSX I used some Mac tool that escapes my memory right now, but it seems you don’t have to do that as Firefox has it built in.

Pres Shift + F2 which will bring up the Firefox CLI. From there type screenshot --fullpage. Be sure to follow the prompts around filename and any other options.

You’ve got your screenshot saved to your Downloads folder.