What to include
For a problem report, the URL that misbehaved is by far the most useful thing — or, if it is not public, a small document that reproduces it. Add the extension version (shown in the footer of the formatted view) and your Chrome version.
A page was formatted that should not have been
This is treated as a bug. Send the URL and what the page actually is; detection is tightened with a regression test for each report.
Do not send private data
Do not paste tokens, credentials, internal URLs, or production payloads. Redact them, or reproduce the problem with a small example instead.