If you can make this as user friendly and functional as Vivaldi Browser's Side Panel feature, Firefox would be my daily driver. Vivaldi's Side Panel feature is something that I expect and use all the time. And is what keeps me coming back to Vivaldi from all other browsers.

今の所快適です。
早くきちんとした機能としてこれが実装されてほしい。調べ物をしながらYouTubeを見るのに便利です。
私はuserChrome.cssを使ってサイドバーの幅を可変にしています。

ただいくつか要望があります。

・コンテキストメニューは通常画面の方と同じ表示にしてほしい。
せめて「進む／戻る」が表示されていたらもっとページ遷移が楽になるので。

・横方向にはみ出した時、横スクロールバーが表示されません。

・firefoxを閉じた時、その画面を残すか選ばせてほしい。


……自分の場合スライドバーは元々ブクマの表示をメインにしていたので、スライドバーを使いつつ画面分割できるのが一番の理想ではあります。
画面分割できるアプリはありますが、JavaScriptを使ったページ（Google翻訳など）だとうまく表示されませんでした。
画面分割機能も開発お願いします。

I use it to keep my task lists open alongside my email+calendar+etc, so it's really a huge help with my daily office work!

Great addon. Some missing option to perfection : some buttons (back, reload) and capability to display more than 25 % width.

nice idea and for a developer it's really helpful. it would be nice if i can open whatsapp messenger on side bar. right now it only show the whats app web page.

Okay But when wanting to have Youtube it misses a portion of the video it will not fit, please do something about this for max stars.

One of the best feature. It should have made to the final release of firefox. It would be great if it had dark mode to be consistent with whole browser.

Instead of this being just a side bar, I want this to be able to use Mobile version of a website (it can do this now... but) + the ability for this to be a a split window. I know this is currently an extension, but the whole idea about using this as an experimental extension is to see if this feature makes sense to be in Firefox natively right? I would want this natively in Firefox if it can work as a:

1. Side view exntension's current capability. Don't remove mobile website invoking capability of the extension. Amazing for testing and other mobile oriented experiences when needed.
2. If it can also work as a split window natively instead of having to rely on an extension.

Fantástica extensión realmente práctica. Yo añadiría la opción de mostrar la versión de escritorio de las webs en el Sidebar y no solo la versión móvil.

Need to keep improving and having updates. Messenger Facebook is inaccessible!!!!

This is an amazing idea and a very handy one. It should be not just developed but considered a Firefox essential piece.
It's great for web-mail checking, mobile version view, quick service checking, rapid social media posting, etc.
Hope it gets the attention it deserves.
Thanks a lot for such a great add-on!

No doubt that this is a great addon, and very useful.
There should be some option to go back on the page as main back button doesn't work with sidebars, that's why I removed one star. I understand this still is a pre -release version so may be they resolve such issues before final release. Thank you Firefox.

Unfortunately firefox doesn't allow multiple side bars, so you can't use this alongside TreeStyleTabs to have two browser panes with one tab sidebar :(