This is a tab manager for Firefox.
It has over 500 commands and around 780 settings.
It can do a lot, and it's aimed to provide advanced features without getting limited.
https://addons.mozilla.org/en-US/firefox/addon/grasshopper-urls/
Some features to mention could be:
Type to filter tabs and filter modes (around 20+ modes like Pinned, Normal, Unread, Loaded, Parents/Nodes, Images, etc)
A Tab Box at the bottom with around 20 modes like Special, Recent, Containers, Playing, which is a widget to show certain kinds of tabs persistently.
A button to go to playing tab. Right clicking this shows a list of all playing tabs.
A button to go to previous tab. Right clicking this shows more recent tabs.
A sidebar with commands you can add.
(Some) bookmark navigation and saving. Bookmark tabs, view bookmarks. (The main focus is not bookmarks but it has some support).
A History mode to find previous tabs.
A titlebar which can be edited to show information dynamically through the Signals system. The Signal system is a simple interface that you can use to send/receive triggers and data from the extension to a python (or whatever) script. In my case I use it to update the titlebar (top bar) with my currently playing song.
Buttons to go to the bottom or top. Mouse gestures to scroll or whatever you map it to.
Keyboard shortcuts, which can be customized or added.
Lots and lots of settings.
Themes, customizable appearance.
Context menus that can be filtered by typing. So if a list has hundreds of items you can type "blue" and it will filter items containing that substring instead of scrolling too much.
A lock screen, which can have an optional password.
A command palette to run commands.
Note taking, on individual tabs or general.
Show Closed tabs. Re-open closed tab.
Tab coloring. Tab tagging. Tab ghosting.
Coloring is giving a color to tabs, these can appear as icons, or as background, or both. These are customizable. Custom colors can be created.
Tabs can be tagged with any amount of tags which can be used to filter certain kinds of tabs, you can filter by tag. There is a taglist which shows tags under each tab (configurable).
Ghosting means the tab's text is obfuscated until you click an icon to restore it. This is in case you don't want some uncomfortable title to be displayed in a public setting for too long.
There are commands to jump to tabs of a certain kind. Jumping means it goes to the next tab, without having to filter it. So you can run for instance the "Red Down" command which goes to the next red tab.
Icons for many states like unloaded, pinned, etc. All icons can be configured.
Many commands and more are created automatically based on settings you make.
Clocks, dates.
Zones. These are separators you can insert anywhere in the middle of the tab list that helps you visually to find what you want. These can be headers or sub-headers. The action when clicking these can be configurable.
Basic Container support to filter by container.
Domain Rules. You can attach rules to specific domains. For example you can change the title or icon of a certain domain.
Move tabs to other windows. Basic window picker.
Different text modes: Title, URL, or both.
Wrap or no wrap on tabs, to display more text.
Command Combos. Make new commands which are a sequence of commands to perform in order. These can have a delay between them. You can then run this on the palette, or put it in the sidebar (favorites) or attach it to any of the many MANY mouse mappings around the interface.
Custom URLs. A list of URLs than can be used to open tabs, can be used in commands.
Icon Pick. An icon that appears on the side of tabs to pick them. With various actions depending if click or right click, or drag. (Off by default).
Some sound effects.
Autoclick. Perform a click automatically by just hovering them with the mouse. Many components can be enabled for this, and the delay is configurable.
Browser Commands. Configure the commands Firefox has access to for kb shortcuts.
Configurable Close Button. Which can autohide.
Create custom favorite filters to filter things quickly. Right click the filter to see recent filters used.
Footer. Show tab count, title/url of current tab. And other buttons for actions like Move To Top or Move To Bottom.
Hover Button. A button that appears when hovering tabs, which can be used to perform actions.
Embed Media. Image, videos, audio, can be displayed by clicking an icon, instead of switching to the tab, which might be useful if you don't want to change the current tab.
Configurable menus throughout the interface.
Pinline. It's a divider that has pins on top and normal tabs on bottom. Can also do actions when clicked and only shown in certain conditions.
Show/hide interface components.
Configurable warnings. For instance define if tabs playing audio should warn when being closed or not, if only closing one or multiple.
And more things that are not mentioned.