Mozilla recently pushed its completely rewritten Firefox for Android to the stable release channel, but gHacks has only now spotted a change that many people might dislike. Just like most Chromium-based browsers, including Google Chrome itself, Firefox has stopped showing the full URL in the address bar, omitting the protocol and the www. subdomain.
As known from Chrome (since version 85), a lock symbol next to the address bar indicates the security status of the connection. When it's locked, you're surfing the website via the encrypted https:// standard, and if it's crossed out, you're connected via an insecure http:// connection. However, it looks like only the www. subdomain is shortened — websites with other subdomains, like outlook.live.com or mail.google.com, are still fully displayed. To see the complete address, you can either tap the lock or the address bar itself.
gHacks also spotted that some bugs were filed on GitHub, asking Mozilla to restore the full address, but so far, they have already been closed — it's safe to assume that the non-profit wants to stick with this design. While regular folks may not care for which protocol and which subdomain is used, it's helpful for power users who prefer to know exactly how they're connected to a website. That said, I can understand that Mozilla and other browser developers want to save as much space as possible on smartphones, which might help display some longer URLs that would've been cut off otherwise.