It ONLY happens with Firefox, and only in google shopping .... Chrome doesn't do it and Edge doesn't do it, and FF doesn't do it on other search engine shopping pages.

I am so annoyed I am switching to Edge until it is fixed.

Start Firefox using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

No, it doesn't do it in Troubleshoot mode, but I don't get a full width page either.

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Go to that message, and use the Undo link to its right.