Twitch.tv websites broken
On Aurora 25.0a2, HTTPS-Everywhere 4.0dev9 completely breaks all streamers' individual Twitch.tv sites and Twitch.tv's site in general. Nearly everything but the basic site navigation shows up blank (no video player, no descriptions) and the chat also doesn't work. Loaded from a third-party site such as speedrunslive.com or teamliquid.org, the video player loads and works, but the chat still doesn't work.
Disabling the extension alleviates the problem and everything works as expected. This does not appear to be ruleset-related, as there apparently are no rulesets for Twitch.tv. This has been reliably reproducible on two PCs I possess and is, by my testing, definitely the only extension responsible the problem. Firefox Beta 24.0b2 also does not work, IE10, though, obviously does (meaning it's not necessarily Twitch's fault). I am not sure which party is ultimately at fault here, but given that Firefox otherwise works flawlessly without the extension, I'm going to guess it's got to be something on HTTPS-Everywhere's side that a recent change somewhere caused to break.
Given the easily reproducible nature of the bug and the fact that Twitch.tv is pretty essential to many people, I'm going to mark this as critical. If I'd know whether this also affects both Firefox 23 and/or Chrome/Chromium, I'd possibly mark it as a blocker.
This does not appear to be MCB-related and disabling the option in about:config doesn't fix the issue. It should be noted, though, that the above-mentioned sites load the video player via a normal HTTP connection. Go to an individual streamer's site, load a VOD and you'll see that Twitch also has SSL-enabled CDN URLs available (which work just as well as the HTTP ones if loaded directly). I am not sure whether Twitch even allows a live broadcast to use SSL, though, but due to the overhead I'm guessing not. Anyway, the VODs and streams themselves work fine if you use their direct URLs. Embedded into Twitch's site, though (and only Twitch's), they don't work anymore.