Because avast is using a entirely other algorithm to create the rating. What is used is explained on the avast blog website as well as in threads on this webboard.
I don't know for sure why the different rating between the browsers - only possibility is it is more popular in Chrome than Firefox, spread across avast users.
For what I've found I learned that an add-on reputation is all about whether an add-on is from Chrome Webstore or AMO (addons.mozilla.org) and users install/remove rate. It's not about security, so scam add-ons for Chrome might get high reputation. And if someone not from the target audience of my add-on installs it by mistake and then removes it - bam! reputation goes down. I've read that despite being good add-on it might have bad reputation, so avast! will propose to remove it. What's the point of that? I don't understand.
I think that avast! thinks, that all add-ons for FF not from AMO is bad. And it happened that my add-on for FF is hosted by github, and add-on for Chrome is published on Chrome WebStore.
P.S.: and captchas are really hard. I changed it ~10 times before I could recognize the letters.
I think the OP means the Chrome store and the avast rating in FF.
You think? I posted the image showing my issue in the first post.
