Firefox 97 has the latest evolution of the combined preview/setup/print experience introduced in Firefox 84. The old code has been removed. There's no going back.

What do you need to change the size of? If you mean changing from Shrink to Fit to a specific percentage, you can find that in the new setup panel if you click "More settings":

I have changed back to Firefox version 96.0.3, but I'm now worried about logging into my bank account using an out-of-date browser. I may change to the latest Firefox ESR release which I think is Firefox 91.6. I included some thoughts about how to change back in my question https://support.mozilla.org/en-US/questions/1367362

There are now several posts about this on the new feedback site connect.mozilla.org (which has replaced mozilla.crowdicity.com). You can access this new site using your Firefox login. I would encourage anyone who has an opinion about this to visit the new site and leave some feedback.