Especially if it isn't a comedy.

You can adjust your update settings as described in this article: Advanced panel - Accessibility, browsing, network, updates, and other advanced settings in Firefox.

I considered temporarily changing the update setting to "Never check for updates" when streaming videos. I am sure that would work, but it does not seem like a permanent solution to me, because I will have to keep changing it back and forth, and hopefully, not forget to do it.

I'm not sure the alternative -- automatically update without notification -- would suit your needs, either. It might be that Firefox would quietly wait for you to restart the browser, but it's possible you would get a notification to restart. Hmmm...

Fortunately, Firefox releases are fairly predictable: once every 6 weeks. In between, there usually are only emergency releases for extreme breakage. If you disable updates and forget to turn them back on, you could make a habit of checking every Wednesday (e.g., Help > About Firefox > Check for Updates).