Thank you, this is the feature I wanted.
However, like Yandex Browser, Whale Browser, Edge Browser, and Vivaldi Browser, closing and opening the window does not keep the content displayed.

best . these things make firefox best . tried firefox after being bored by chromium and now never going back there

This is perfect for quickly throwing an email I am referencing in the sidebar and copying the data over!

How to make side panel resizable:
Updated instructions for Feb 2024 (I'm on Firefox version 123)

- Go to about:support
- in Application Basics section find row called Profile Directory, click on Open Directory button
- Close all firefox running instances
- In that folder, find xulstore.json and open it with a text editor
- Find where it says "sidebar-box":{
- inside those brackets look for "style":
- inside this find width: and replace with the following:
width: 50%; max-width: none !important; min-width: 0px !important;

- if you did it correctly it should look like this: "style":"-moz-box-ordinal-group: 3; order: 1; width: 50%; max-width: none !important; min-width: 0px !important;","checked":"true"

- save the file and close, open Firefox and have fun :)

I hope to see Side View fully implemented natively in Firefox soon.

But it isn't useful as is, with the limited width. I had to fix this with this guide:
https://superuser.com/questions/1276800/customize-the-maximum-width-of-the-firefox-sidebar

Required a change in about:config for me:
(toolkit.legacyUserProfileCustomizations.stylesheets = true)

this what im looking for ! its link split screen in microsoft edge i love this extention!

Can someone maintain this plugin?
Some important features are missing:
* Ability to add multiple website icons in link or right panel.
* Click on any icon to open its website in the panel.

They are useful for workflow!

They would be like Vivaldi side panel

If I had known about this feature, I would never have left Firefox for Edge. (Please add this as a built-in feature.)

Edge had another very productive feature called Web Select, which allowed users to copy text with formats. It was based on their built-in web capturing feature, but unfortunately, they deprecated it. Now users are upset, and Bing Chat is not a very useful feature to keep people with Edge.

Please add a Web Select-like feature to Firefox Capture. This is the last thing I need from Firefox. Great work! You are the pioneer of browsers. Thanks!