This is the first time I can remember writing a review of an extension. I don't use many, but I use this one every day and it does exactly what I need it to. I mostly use it in batch scripts so that I can open up a set of webpages in the right containers at the start of my work day.

One note to help fellow Windows users: you may need to specify the full path to Firefox to get this to work. On my machine that's C:\"Program Files"\"Mozilla Firefox"\firefox.exe "ext+container:name="MyContainer"&"url=https://mozilla.org'

Also, as others have mentioned, if your container name has spaces in it, swap those for %20. Some other special characters will use similar syntax. You can use this site to convert the name properly: https://www.urlencoder.org/

Thanks for making this!