Mac OS X Yosemite – How to disable autoresizing tabs in Safari 8

Here's a way how:

1. Install EasySIMBL, which is an extension manager for Mac OS X apps and move it to an Applications folder.
2. Open it up, and make sure to check Use SIMBL

3. Download CosyTabs plugin, extract it and finally drag & drop .bundle file into the EasySiMBL application.

4. Then simply restart Safari, and you're done!

Please note that if EasySIMBL is not working for you (versions older than 10.10.4 b4 still work) you can download SIMBL which EasySIMBL is based on.  However the changes made to EasySIMBL prevent it from working on newer systems. It's suggested to try EasySIMBL first thou, as it may get fixed by the author by the time you read this. The difference is that SIMBL has no graphical interface so some steps have to be done manually.

Quick SIMBL instruction below:

1. Download SIMBL
2. Unpack SIMBL.zip package
3. Use SIMBL-0.9.9.pkg to install application (just follow installer with no changes needed)
4. After it's successfully installed simply copy plugins into /Library/Application Support/SIMBL/Plugins for all users, or ~/Library/Application Support/SIMBL/Plugins for just your account.
5. That's it.
6. After Safari restart everything should be working again. That is on Mac OSX Yosemite.

For Mac OSX El Capitan things get little complicated with the introduction of Rootless (as Apple calls it) or SIP (System Integrity Protection) mechanism. You can read about it on Total Finder. We've covered How to get SIMBL working in Mac OS X El Capitan after upgrade in one of the newer blog posts. After following this a bit complicated procedure simply follow the steps described above to disable autoresizing tabs in Safari 9.