There has been a discussion about Firefox 57 in several threads here. @paulderdash suggested to create a new thread, though, which specifically covers FF 57 and webextensions. Okay, I'm trying to summarize the most important changes with links to resources which provide more information. Firefox 57 will be released on 2017-11-14. It will be a milestone release as it will be the (preliminary) end of a massive overhaul with significant changes in its architecture. The most important changes are: Multiprocessing implemented via the Electrolysis (or e10s) project which aims to make FF more stable, more secure and faster. The most important part is probably the introduction of multiple content processes. It seems that it is planned to determine the number of processes depending on the amout of available RAM. However, you can manually choose the number with dom.ipc.processCount in about:config. Similarly you can also choose to run add-ons in their own process(es). Local file access is also moved to an own content process via browser.tabs.remote.separateFileUriProcess Multiprocessing is the basis for sandboxing and process separation. In FF 57 Nightly Level 3 is enabled. This should bring FF more or less on par with Chrome. Quantum is "Mozilla's project to build the next-generation web engine for Firefox users, building on the Gecko engine as a solid foundation. Quantum will leverage the fearless concurrency of Rust and high-performance components of Servo to bring more parallelization and GPU offloading to Firefox." This will increase both performance and security as those components are written in the Rust language which will prevent many pitfalls (like the infamous buffer overflows) often resulting in security flaws. Btw, here's a very interesting article about Quantum CSS (aka Stylo). Firefox will get a new design called Photon. A newer blog post with some nice pictures is here. The most controversal change happens in the extension system. Legacy XUL-based add-ons won't run anymore. Only webextensions will be compatible with FF 57+. The rationale for this decision is, at least, two-fold: 1. As legacy add-ons had unlimited write permission for about:config, this often caused incompatibilities and unstabilities in the past. This is no longer possible with webextensions as they communicate with FF exclusively via specific APIs. 2. Webextensions are more secure as they are only allowed to do what is explicitly specified in their permissons and what is possible via the APIs they are using, and they can run in their own process(es) which also enhances browser stability. Note also that the webextension APIs apply a rather strict Content Security Policy (CSP) to all add-ons. The downside of this change is that quite a number of beloved legacy add-ons won't work anymore and cannot be rewritten as webextensions. 3 hints: On AMO you can find the list of add-ons which are compatible with FF 57+ on https://addons.mozilla.org/en-US/firefox/search/?tag=firefox57 . This list is getting larger and larger (right now about 3,800 results), and chances are that you can find replacements for some legacy add-ons. Note that some well-known add-ons like uBlock Origin and uMatrix are not yet on that list but are already available as webextensions in the development channel on their AMO sites. There is this spreadsheet which suggests alternatives for legacy add-ons. Many additional APIs are already approved by Mozilla and many are still under discussion. Many of them will probably land in FF 57 but some of them might only get implemented after FF 57 is out, so chances are that in the future add-ons will be available for which necessary APIs are still missing today. A nice collection of webextensions related to security and privacy compiled by @siric is available here. Other collections with webextensions can be found here. Not directly related to above big overhaul but still very important is the Tor Uplift Project which aims "to land all Tor Browser patches so that Tor can directly use Firefox main trunk instead of a fork". These patches will considerably improve the resistance against fingerprinting and tracking. Please add more info as necessary!