Quoting Think Twice Before Installing Any Chrome Extension (Arpit Kumar for TechRaga).
These extensions are not checked by Google for possible malicious behaviour. ... The most unfortunate thing is that the Chrome team has no intention to implement an approval process for the items available at Web Store. I raised this issue earlier, but then the Chrome team said, “We’ve purposely avoided having a pre-review process for the extensions gallery / Chrome Web Store.”.I wonder if some kind of community-driven process could be instituted for this.
Thankfully, Mozilla is much careful about the Firefox users – and all add-ons are tested manually before they go public on AMO. Certainly, it takes long time to get approved but this ensures best and safe user experience.