The finished version, Firefox 41, offers a number of tweaks, but its main claim to fame is an enhanced instant messaging (IM) feature. Firefox 42 is all about making it harder for sites to track people who visit them.
One of the best things about the Mozilla Foundation, and its Firefox browser, is the "openness;" the beta version is open to anyone who cares to tinker with it, as long as they understand that it may have some rough edges. (You can download Firefox 42 here.)
I tried both new versions on Windows 7 and Windows 10 and didn't notice any significant problems. I've used Firefox as my main browser for years, and although it's not as popular among Web surfers as it once was, it gets the job done without unnecessary drama. If you already use Firefox, I see no reason not to upgrade to Firefox 41. Ordinarily, I don't encourage people to use beta products, but my experience with Firefox 42 has been smooth so far. It's worth a download, but keep in mind that issues certainly could arise, and Mozilla might add or delete certain features.
A while back, Mozilla built a new video communications feature it called "Hello." Firefox users can now use Hello to send and receive IMs during video calls in the browser on Windows, Mac and Linux. The people on the other end of those calls or chats do not have to use Hello. You can simply send an invitation from Firefox to the recipient via email, and if he or she is using Chrome, Opera or Firefox and chooses to accept, you're connected. Unfortunately, the feature only currently works in the desktop version of Firefox.
The release also includes updates that let users personalize their Firefox accounts with photos, and sync seems to work a bit better, so it's easier to share browsing data, such as passwords, bookmarks, and history, across your various devices.
The private modes in most of today's browsers purposefully don't save your history. Firefox 42 takes private browsing a step further. From Mozilla:
The feature also blocks some ads, but that's not its primary purpose. If ads don't contain trackers, Firefox 42 will load them.
The new private browsing mode also has a "Control Center" that provides quick access to all of Firefox's security and privacy controls. It's a notable enhancement, because it makes it easier for users to take advantage of the safeguards. And because some websites won't load if you disable tracking, Mozilla added a button to the toolbar that lets you turn off the no-tracking feature for individual sites.