It's because they have not updated the github page, read here for more info:
https://github.com/norio-nomura/EasySIMBL/issues/25
https://github.com/norio-nomura/EasySIMBL/issues/26
https://github.com/norio-nomura/EasySIMBL/issues/28
This is a collection of OS X Tweaks that I put together.
While looking around for tweaks I noticed some interesting ones don't have compiled versions available.
DarkDock and Afloat for example had no compiled version/releases so unless you have xcode (8GB) to build the project yourself there was no simple way to get the tweaks.
What I've got up so far:
Lots of my favorites are already posted, but here’s one I’m sure many people will appreciate: Safari Tab Switching. It’s not an extension per se, but what it does is simple yet amazing... cmd+number to switch to tab!
Install it and use with bundled SIMBL, or extract it and use with EasySIMBL like I did.
I find EasySIMBL better. I believe its injection mechanism is more reliable (though still requires a manual relaunch of LaunchAgents to be injected), plus it has a neat gui.
SafariStand works fine in El Cap. You just have to disable SIP, manually install it with classic SIMBL instead of the GUI-based EasySIMBL, then you good.
https://github.com/norio-nomura/EasySIMBL/issues/26#issuecomment-117028426
http://i.imgur.com/iExwtN8.jpg
Just install the version for Safari 9 on Yosemite, works fine. The one bug is that favicons on regular tabs don't show if Safari is in fullscreen mode, but the sidebar tabs still work. Each time you update OS X Stand won't load the first time you open Safari, then will work again on the second load. Haven't seen any other issues.
I used EasySIMBL + SafariStand. SafariStand can turn on favicons in tabs (along with other functionalities).
If you use El Capitan: EasySIMBL is not compatible with OS X 10.10.4. So use original SIMBL for now.
Sorry, I was on the thread saying that that worked on 10.9.5 with the SIMBL fix.
If you have not yet doe so, look at github. May help.
Just install EasySIMBL, download the MenuBarHider-1.0.zip and drag it into the EasySIMBL plugin folder (or the installed plugins list in EasySIMBL).
I don't use it, but MiddleClickClose is "a SIMBL plugin that allows you to close tabs in Safari in OSX by middle clicking anywhere on them." Requires EasySIMBL.
To get favicons+better tabs in Safari, 1) Download EasySIMBL by clicking the "download zip" link in the rightmost column. 2) Download SafariStand from this link. 3) Run EasySIMBL, check the 'use EasySIMBL' box in the top corner, then drag SafariStand into it. Boom.
Safari Stand is nice because not only does it widen the search bar but it also makes your tabs evenly sized. Great tweak in general.
I think Saurik has thrown around the idea of substrate for Mac but it hasn't really happened. There is a tool called EasySIMBL (https://github.com/norio-nomura/EasySIMBL) that allows code hooking on OS X and is pretty similar to substrate's purpose. I think type status for Mac uses it (or did at one point). So yes, it's completely possible, it just hasn't really happened.
Apparently Chrome has a white list of allowed bundles.
The original SIMBL package is on the white list and should work, but easySIMBL isn't on the white list.
It looks like they are working on a fix: https://github.com/norio-nomura/EasySIMBL/issues/12
I've got a precompiled version here: https://dl.dropboxusercontent.com/u/3035075/Menufela.bundle.zip (8kb).
I also recommend using EasySIMBL to install the plugin.