Hi, your Firefox identified itself as running on Mac OS X 10.13. Is that right? The Extended Support Release of Firefox 115 is the last version/series for your version of MacOS. ([[Firefox users on macOS 10.12, 10.13 and 10.14 moving to Extended Support Release]]) Have you considered upgrading MacOS? Unlike a normal update, this requires a separate step. If you go to the Mac App Store and search for Sequoia (https://apps.apple.com/us/app/macos-sequoia/id6596773750?mt=12) it should tell you whether your Mac is compatible. Right now, if you can run Sequoia, Ventura, Monterey, Big Sur, or Catalina, you can update to a newer version/series of Firefox.

Short version is you need at least macOS 10.'''15''' (ten.fifteen) to run Firefox 116.0 or later including the current Firefox Release.