In Safari 12, Apple removed the possibility of downloading 3rd party extensions that weren't available on the Safari Extension Gallery.
Hopefully, there is a way to bypass this issue, and I’ll show it to you in this story.
First, let’s download the extension.
Once, it’s downloaded, you should have the following file in your download folder:
Now, let’s open this weird app (if you’re not a developer of course 😊) called Terminal. To open it, just do a simple Spotlight search by hiting Cmd+space.
Once it’s open, type the following line and hit enter:
cd Downloads
This will tell the app to open your Downloads folder.
Then, you’ll copy the following line, but you’ll replace “Muzli” by the extension you’re trying to download.
xar -xf Muzli.safariextz
This will unpack your extension.
Now, open Safari, and hit Cmd+, . This will open the settings window. And navigate to Advanced.
Now, tick the last checkbox, this will enable development mode.
Then in the Development menu, go to the extension builder.
Once you’ve opened the extension builder, you should see a window popping up.
Now, you’ll select the unpacked folder that will have at the end of it’s name .safariextension.
Once you’ve opened the extension, just click on the execute button to install your extension.
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