Firefox Community Forum

I'm using Firefox as my default browser, and I saw a link preview for YouTube (on tumblr, if it matters) that displayed the message 'Your browser is deprecated. Please upgrade' instead of the actual video title. What does this mean?

How do I completely uninstalled Firefox and revert back to the previous version, and turn off auto updates?

https://support.mozilla.org/en-US/questions/1569387#answer-1804235