Common licenses specifically go out of their way not to imply such a contract. This is the start of the all-caps portion of the MIT License [0]:
> THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO […] FITNESS FOR A PARTICULAR PURPOSE
…and the GPL has nearly the same text in section 15. [1]
Yeah, but also common licenses are set by the distributor. (which they're also evidently free to secretly change?)
I want the other side of the deal: a default license implicit in the existence of software that can't be traded away without an explicit contract that involves something like an exchange of money, which a federal agency will safeguard against violations of. If an extension changes its behavior nefariously people should go to jail. If Google safeguards an extension that changes it's behavior nefariously then Google should go to company jail. (or, like, be fined and forced to comply).
(admittedly, this is hopeless idealism. But still.)
> THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO […] FITNESS FOR A PARTICULAR PURPOSE
…and the GPL has nearly the same text in section 15. [1]
[0]: https://opensource.org/license/mit/
[1]: https://www.gnu.org/licenses/gpl-3.0.html#section15