This looks good.
I edited it a bit for grammar and stuff, but also revised two of the sentences to now say
the following.
Neither the developers nor the Wikimedia Foundation
are responsible for anything being leaked. By using this extension, you agree to indemnify
the aforementioned parties and hold potential negligence by developers harmless.
This message is added automatically to all extensions of this nature and may not reflect
the actual security status of this extension.
I am not a lawyer, but as far as I am aware, an explicit waiver of negligence is required
for a defense to a negligence lawsuit in U.S. courts. In fact, the word negligence being
specifically stated will make any defense much stronger. Maybe this should be checked with
WMF Legal. This sentence has been added to protect the developers of the extension.