Firefox is a multi-process program. What that means is that there are multiple processes running at a time. When it was first added to Firefox, this feature was called ''Electrolysis'' or ''e10s''. This allows Firefox to separate certain tasks and has various security and performance benefits. For example, the main Firefox program runs in a process, your browser add-ons run in another process and the websites you visit run in their own process as well. Now assume that a website you visit freezes. In the past, when Firefox was just running in one process, that may have crashed the entire browser. But now, you would most likely get an error message that says the tab has crashed and it would allow you to reload that tab without having to restart the entire browser. The Mozilla blog post [https://blog.mozilla.org/addons/2016/04/11/the-why-of-electrolysis/ The “Why” of Electrolysis] from April 11, 2016 does a good job explaining the benefits of having a multi-process program, as does the [https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Multiprocess_Firefox/Motivation Motivation for Multiprocess Firefox] page on MDN. Many other programs, including other internet browsers are multi-process programs. If you go to the Firefox settings page and scroll down to the '''Performance''' section, you can uncheck the '''Use recommended performance settings''' option, which will give you a little more customization. There you can set the '''Content process limit''', which will restrict how many processes Firefox can use for displaying the websites that you visit. See [[Firefox's performance settings]]. However, it's generally recommended to leave the '''Use recommended performance settings''' option checked and allow Firefox to adjust the settings on it's own based on your system. Hope this answers your question.