Stop opening new tabs when you update
While I like your app for the most part, its tendency to open a tab to your home page to brag about each new update is unacceptable. It doesn't care if you're watching a video, or doing something else that should not be interrupted, it just steals focus any time it feels like it. Do like other apps: put a discrete notification up on the Firefox menu bar when an update is pending, and wait for users to click it before proceeding, or better yet, do your updates silently, when the browser is closed or opened. You don't need to keep advertising to me. I've already installed your app. In fact, the one thing that might make me dump it is continuing to do this, after multiple users have told you how annoying it is.
The updates are handled by Mozilla, you can disable auto-updates for your setup from addons manager see- https://blog.mozilla.org/addons/how-to-turn-off-add-on-updates/ but it will result in obsolete version of the addon.