As a preliminary side note, I find it "funny" that some users who seem to care about their privacy still use Google services, Gmail above all. Dudes, think again (if I may) and find yourself equivalent online services that do care about your privacy and respect it.
I may suggest the "De-google-ify Internet" campaign (https://degooglisons-internet.org/) among others.

Regarding Canvas Defender: after using it for a few weeks, I suddenly wondered about its license... After checking, it's apparently released under the BSD-2-Clause license (according to Mozilla) and its source code is "available" (by unpacking the extension xpi file I believe ?). But this is about all. Nowhere on https://multiloginapp.com/canvasdefender-browser-extension/ could I read anything relating to the license of this extension. I don't know what to think about this lack of clarity. So for the time being, I'll stop using this extension, until Gravity Development LLC clarifies that point (ideally, their FAQ should mention which license protects their extension and a license file should be enclosed in the xpi file).