Twitter/Mastodon don't respect bottom rounded corners

[phillipprado]

Describe the bug
If you navigate to Twitter or Mastodon, the bottom corners appear to break out of the browser's rounded corners, making them pointed.

To Reproduce

1. Go to twitter.com or many mastodon instances like infosec.exchange
2. Look at the bottom corners of the browser

Expected behavior
Browser corners should still stay rounded as per the theme's corner radius.

Screenshots
Twitter's bottom right corner:

Mastodon's bottom right corner:

Setup information

• OS: Ubuntu 23.10
• Installation method: Flatpak
• Firefox version: 125.0.1
• Theme version: v124
• Optional features enabled: gnomeTheme.hideSingleTab, gnomeTheme.systemIcons

Additional context
It doesn't matter if you change the Twitter theme to dark or light mode, the issue is still there. It's hit or miss which Mastodon instances are affected.

[rafaelmardojai]

Bottom rounded borders come from Firefox and still have some bugs/regressions. Nothing we can do.

https://bugzilla.mozilla.org/show_bug.cgi?id=1850827