Hello everyone,

Is it possible to add a sidebar to Tor browser without losing the fingerprint defense?

Ctrl-B works here. Is there a problem?

Does it compromise the fingerprint defense?

Does what compromise the fingerprint defense?
Can't you compose a valid Linux question? Please read the first link in my signature.
While I have an inkling what it is you're asking, I'm not playing the guessing game.

An obvious answer: go to https://amiunique.org and compare the fingerprint of your browser with and without the change you've made.

TBH, I don't understand your question. What is the fingerprint defense, and how it can be compromised?

That said, if you have Javascript disabled, no web site can determine much about your browser beyond what is submitted in HTTP headers (user agent, content encoding, referrer, etc.).

Tor Browser uses a Firefox setting which locks the window to specific sizes to help reduce fingerprinting by unusual resolutions / window sizes.

Enabling that setting prevents the browser from being resized or maximized.

Opening a browser sidebar changes the width of the document, which presumably can be used to differentiate from someone who doesn't.

None of this depends on JavaScript being enabled, so disabling JavaScript is not a solution (besides which, disabling JS would also present a different fingerprint).

The best place to ask about this is somewhere where all the above doesn't need to be explained.

There's various options listed at https://www.torproject.org/contact/