If you made videos stop playing, users could switch to Chrome as a fix when their gifs stopped playing.
Firefox 57 changed to using a more limited extension system like Chrome already had, so it's not like users could jump ship to Chrome to get back Firefox 56's more powerful extensions.
You may not have liked or agreed with that change, but I don't think it actually drove people to alternative browsers. If anything they might have said "Well, I have to going extension browsing anyway to find new ones that work, maybe I'll take a look at the options in Chrome too."
Firefox 57 changed to using a more limited extension system like Chrome already had, so it's not like users could jump ship to Chrome to get back Firefox 56's more powerful extensions.
You may not have liked or agreed with that change, but I don't think it actually drove people to alternative browsers. If anything they might have said "Well, I have to going extension browsing anyway to find new ones that work, maybe I'll take a look at the options in Chrome too."