Second Sidebar for Firefox

A Firefox userChrome.js script for adding a second sidebar with web panels like in Vivaldi/Floorp/Zen but better.

Motivation

There are many forks of Firefox, but I prefer to continue using the original browser. However, I have also tried other browsers such as Vivaldi, Floorp and Zen. I also miss the feature of having a decent sidebar with web panels, which is why I decided to create my own version, with blackjack and hookers.

Demo

fss_demo_v1.3.mp4

Features

⚠️ Warning: data-intensive GIFs under spoiler ⚠️

Adding new web panel Left-click on the Plus button. Enter the web address. The current address will be automatically inserted into the field. Choose Multi-Account Container if you want. Press Enter or click on the "Create" button. A new web panel will be created with default settings.
Pinning and unpinning the web panel Depending on your needs, you can pin the web panel to the side of the web page or make it appear on top of the content.
Mobile view and zooming There is an option to open the website using the mobile user agent. There are also buttons to zoom in and out of the content.
Unloading the web panel from memory To save memory, you can manually unload the web panel using two methods: the toolbar button or the context menu.
Web panel settings Here you can change the following: Page address. After changing the relevant field, please wait one second for the changes to be temporarily applied. They will be saved or canceled depending on your next action. Multi-Account Container. Favicon address. The same as for the page address. Web panel type: floating or pinned. Use mobile User Agent. Load into memory at startup: automatic loading of the web panel. Unload from memory after closing. Hide toolbar: "headless" web panel. Zoom. Position of the web panel button. All changes are applied instantly, but can be rolled back by clicking the "Cancel" button or by losing focus. They are saved only after clicking the "Save" button.
Deleting the web panel There is confirmation of the deletion, so you don't need to worry about accidentally deleting the web panel.
Sidebar settings Here you can change the following: Sidebar position: left or right. Sidebar width (padding). Floating web panel offset: distance between sidebar and floating web panel. New web panel position: before or after "Plus" button. Container indicator position: which side of web panel button to color. Hide sidebar in popup windows. Auto-hide of back and forward buttons from toolbar. All changes are applied instantly, but can be rolled back by clicking the "Cancel" button or by losing focus. They are saved only after clicking the "Save" button.
Customization You can customize the Second Sidebar like any other toolbar in Firefox: https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars. Moreover, you can also move your web panel buttons to other toolbars!

Install (fx-autoconfig)

1. Install fx-autoconfig.
2. Copy the contents of the src/ directory (second_sidebar/ and second_sidebar.uc.mjs) into chrome/JS/.
3. Clear startup-cache.
4. Have fun!

If you use another loader

Use a wrapper script provided by @dimdamin: #5.