Add native support for user-defined web panels / custom websites in the sidebar (like Vivaldi / Opera web panels)

[amirabbas]

Hello Mozilla team,
I really love the new unified sidebar in recent Firefox versions (bookmarks, history, synced tabs, AI chatbot, etc.), but one very useful feature is still missing compared to browsers like Vivaldi, Opera, Edge (Collections sidebar), and many Firefox forks (Floorp, Zen, etc.):
The ability to add and pin any custom website / web page directly into the sidebar as persistent panels.
Many users (including myself) use this for:
WhatsApp Web / Telegram Web
Personal dashboards / university portals / email / calendars
Reference sites (Wikipedia, dictionaries, Notion, Google Keep, etc.)
Monitoring tools (price trackers, weather, crypto, etc.)
Right now we have to rely on third-party extensions (like Page Sidebar, Open Link in Sidebar, custom sidebar_action extensions), userChrome/user.js hacks, or separate windows — none of which feel as clean, performant, or integrated as native support would be.
Suggested implementation ideas:
Add a "+" or "Add website" button inside the sidebar
Right-click on any tab / link → "Open in sidebar" / "Pin to sidebar"
Allow pinning multiple custom panels with custom names, favicons, reload intervals, dark mode respect, etc.
Keep existing sidebar tools (bookmarks/history/etc.) and add a separate "Web Panels" section
Optional: support for vertical tabs + web panels side-by-side
This single addition would bring Firefox much closer to power-user workflows that Vivaldi and Opera already offer natively, and would reduce the need for many workarounds/extensions.
Thank you for considering this it would make Firefox even more competitive for productivity users.
Best regards,
[AmirAbbas] 

[Jon]

Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.

[Fabs_Bro]

+1 from me. One requirement I'd like to add: the panel should stay loaded in the background when the sidebar is collapsed or another panel is selected.

My use case is a music player (Deezer, Spotify, YouTube Music). Today an extension sidebar (sidebar_action) is destroyed as soon as the sidebar is closed, so the music stops. That is the main reason I can't replicate the player sidebar from Opera GX in Firefox. Embedding such sites in an extension sidebar also fails because of X-Frame-Options / frame-ancestors, so extensions have to rewrite headers and cookies just to get a login working.

So besides adding custom websites, please make the non-unloading behavior part of the design. Optional but nice: a mute toggle and a mobile user agent per panel.