Show source code (ctrl-u)
ctrl-u no longer seems to show the source code for the page just downloaded, but appears to resend the request to get the source code (again). I've a page which results in a database insert on the server. I view the source code of the reply page, the insert has then occured twice. Previously I'd noticed that ctrl-u caches the source code, so even if the server process was changed, and the page recalled, ctrl-u still showed the old source code unless it was refreshed.
ప్రత్యుత్తరాలన్నీ (2)
You could (optionally, once enabling 'Work offline' mode) save the current page (Ctrl+S), then rename the HTML file extension (in File Explorer app) as a TXT file, right click it, and re-open it with Firefox. It should show the source code without having to re-download it. I don't know of another work around unfortunately.
Note that you can possibly use "CTRL+A" and View Selection Source. There is also the page inspector as part of the developer tools that you can use to get the source (HTML tag -> Edit as HTML).