Browser extension doesn't help any scammer to steal your money. This news could be fake news to downtrend of browser. Why Top popular browser do it, when this apps has trusted users. Especially Google doesn't want to vanish own logo trust which they gained after long fight. I heard that Google and Mozilla already removed some fake extension from their browser.
There is a contradiction since you said fake extension are removed by Mozilla and google, that means the scammers were able to add fake extension and the browser needed to remove them after identifying them to be fake, if you are storing your coins make sure you keep that in a external device which is not connected to the internet.