1) All extensions in the browser are open source - you can look at the source code of version 0.884 and make sure that there is no malware code there.
Even easier - you can compare the code of versions 0.883 and 0.884 and make sure that only the link was added.
2) All extensions on addons.mozilla.org are automatically checked for code. If there was something suspicious in the new version, the version would be blocked.
3) I have no opportunity to test version 0.884 under win7, but I ran the same version in Chromium and this is what the Chromium task manager showed:
https://ibb.co/6vLqwRV
There is no INSANE CPU usage.