Mozilla has moved to a release schedule similar to Chrome's and has maintained a consistent release cycle since. It does not usually go away unless there is a serious problem. Well, there is a serious problem. Mozilla recommends that all Firefox users update the latest version of the browser as quickly as possible. The company has just become aware of a zero day exploit that affects Firefox, which means Negative Internet forces are actively using it.
The latest version and the only one that protects you from the bug is v67.0.3. You can see which version you are using by opening the menu, clicking Help and selecting "About Firefox". The browser should invite users to update, but you can do it manually if your browser is not part of the latest version, simply type "update" in the search bar.
Mozilla has specifically avoided providing many details about the flaw. He only says that he knows that there are active attacks in nature, so he probably wants users to be updated first. Otherwise, it could make things worse.
Firefox has managed to avoid frequent and urgent updates. The last one took place in 2016, when it was corrected for a zero-day exploit that could anonymize users of the Tor network.