That's not to say this is strictly a security patch release (though most of the patches for the final Firefox 52, 52.9, are in this beta). The big feature I did want to get in FPR8 did land and seems to work properly, which is same-site cookie support. Same-site cookie support helps to reduce cross-site request forgeries by advising the browser the cookie in question should only be sent if a request originates from the site that set it. If the host that triggered the request is different than the one appearing in the address bar, the request won't include any of the cookies that are tagged as same-site. For example, say you're logged into your bank, and somehow you end up opening another tab with a malicious site that knows how to manipulate your bank's transfer money function by automatically submitting a hidden POST form. Since you're logged into your bank, unless your bank has CSRF mitigations (and it had better!), the malicious site could impersonate you since the browser will faithfully send your login cookie along with the form. The credential never leaked, so the browser technically didn't malfunction, but the malicious site was still able to impersonate you and steal your money. With same-site cookies, there is a list of declared "safe" operations; POST forms and certain other functions are not on that list and are considered "unsafe." Since the unsafe action didn't originate from the site that set the cookie, the cookie isn't transmitted to your bank, authentication fails and the attack is foiled. If the mode is set to "strict" (as opposed to "lax"), even a "safe" action like clicking a link from an outside site won't send the cookie.
Same-site cookie support was implemented for Firefox 60; our implementation is based on it and should support all the same features. When you start FPR8b1, your cookies database will be transparently upgraded to the new database schema. If you are currently logged into a site that supports same-site cookies, or you are using a foxbox that preserves cookie data, you will need to log out and log back in to ensure your login cookie is upgraded (I just deleted all my cookies and started fresh, which is good to give the web trackers a heart attack anyway). Github and Bugzilla already have support, and I expect to see banks and other high-security sites follow suit. To see if a cookie on a site is same-site, make sure the Storage Inspector is enabled in Developer tools, then go to the Storage tab in the Developer tools on the site of interest and look at the Cookies database. The same-site mode (unset, lax or strict) should be shown as the final column.
FPR8 goes live on June 25th.