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!

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.

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!

great productivity booster!

This is a great Addon. So far so good.
Feedback
In any YouTube video, I can't find horizontal scroll bar. Also there are two huge horizontal black bar. (What I'm trying to say is that the Addon is unable to adjust according to the video's aspect ratio.
Again, great Addon.

very useful extension :)

Love this feature, thanks! Am so glad I discovered it. A bit concerned that Firefox Test Pilot seems to have ended (before I even discovered it). Hope that this excellent add-on does not disappear.

Great tool for developers! You can see the desktop and mobile versions of a page in one window.