On loading an url in a tab, it immediately shows a firefox error (I don't know how to unlocalize it... sadly): "Beim Laden der Seite https://twitter.com/___GreenTea13/status/1308612227449016321 wurde gegen das Netzwerkprotokoll versto脽en. Dieser Fehler kann nicht behoben werden."
The inspector shows this error message on the console: "Fehler beim Laden von 'https://twitter.com/___GreenTea13/status/1308612227449016321'. Ein ServiceWorker hat eine mit 'TypeError: NetworkError when attempting to fetch resource.' abgelehnte Promise an FetchEvent.respondWith() 眉bergeben."
The page is loaded.
When I disable the account container plugin, open a new tab and paste the url, the page loads. At the time of this test it was the only active extension, so this should have an influence on the faulty behaviour.
I have the same issue. I had a container dedicated to twitter. A workaround was to remove this container and create a new one.
The same happens here... what solves is reloading the page holding SHIFT (SHIFT+CTRL+R), then the page loads correctly for some reason. Every time.
This only happens to the container where I'm logged on Twitter. Other containers are able to load the Twitter page correctly.
Firefox for Fedora 81.0.1 (64-bit)
A screenshot of the error:

Can confirm I have the same issue on Windows (64bits) too, so this isn't just an issue on the linux versions
Same problem on MacOs Catalina (64bit)
This was somehow fixed. You should close
This was somehow fixed. You should close
Yes, this issue is very likely not specific to the multi account container extension, it is more like the issue tracked on bugzilla as Bug 1662925, landed in Firefox 83 and uplifted to Firefox 82.
Most helpful comment
The same happens here... what solves is reloading the page holding SHIFT (SHIFT+CTRL+R), then the page loads correctly for some reason. Every time.
This only happens to the container where I'm logged on Twitter. Other containers are able to load the Twitter page correctly.
Firefox for Fedora 81.0.1 (64-bit)
A screenshot of the error: