macossafarisafari-extensions
I am looking for a "tabs decluttering" app for Safari like OneTab Chrome Extension
How OneTab Works
Whenever you find yourself with too many tabs, click the OneTab icon
to convert all of your tabs into a list. When you need to access the
tabs again, you can either restore them individually or all at once.When your tabs are in the OneTab list, you will save up to 95% of
memory because you will have reduced the number of tabs open in Google
Chrome.
If you have Alfred 2, there is a workflow for selecting Safari tabs by typing. It includes tabs from all windows, but it doesn't group them by window.
If you really mean by automatically opens in task bar as a Browser icon displays a the little icon on top of it in the Dock (Handoff app icon in Dock ), and when you click it it opens the same page you are viewing on the other Mac.
then this is nothing to do with iCloud.
This a feature called Hand off. Have a read here
When your Mac computers and iOS devices are within Bluetooth range of each other (about 33 feet or 10 meters), they can automatically “hand off” what you’re doing from one device to another. For example, you can start writing an email in Mail on your iPhone, then instantly pick up where you left off in Mail on your Mac.
Handoff works with several apps that come with OS X Yosemite and iOS 8: Calendar, Contacts, Mail, Maps, Messages, Notes, Phone (iOS only), Reminders, and Safari. It also works with Keynote v6.5, Numbers v3.5, and Pages v5.5 for Mac, and Keynote, Numbers, and Pages v2.5 for iOS. Third-party apps may also work with Handoff.
Best Answer
Here is a native way of doing it without the use of any extensions.
In Safari, under the "Bookmarks" menu, there is an option for you to "Add Bookmarks for These X Tabs...". If you click on it, you will be prompted to save these tabs in the current windows as bookmarks. You can assign them to a Folder and give it a Session Name.
When you do want to resume the session, you simply go to the bookmark folder, right click on it and select "Open in New Tabs".
The beauty of this methods is that, if you have iCloud sync enabled, you will be able to resume your saved sessions across all your Apple devices.