Mozilla and Opera aren't viable because of Chrome. Chrome is arguably more polished because Google pours more money into its development, more readily available because Google can lobby/buy/enforce its inclusion as the default browser, and free because Google makes money from the information it collects through it.

You can't compete with Chrome when your primary merit is simply not being Google. Forcing Google to spin-off Chrome should have been done earlier though, before Microsoft had a stake on the engine. Now additional steps need to be taken to ensure that spinning off Chrome will not actually kill competition; with an independent Chrome, we can count on Google cutting down on Mozilla's funding since Google wouldn't be any longer in danger of being ruled as a browser monopoly.