There is a known issue with WindowBlinds that causes crashing in Firefox. We are working with them to fix the problem. In the meantime, here’s what you can do to continue using Firefox:

Option 1: Disable WindowBlinds for Firefox

See the WindowBlinds support article, How can I temporarily exclude a program from being skinned? for instructions.

Option 2: Disable hardware acceleration in Firefox

To turn off hardware acceleration in Firefox:

1. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings.
2. Select the General panel.
3. Under Performance, uncheck Use recommended performance settings.
   Additional settings will be displayed.

   

4. Uncheck Use hardware acceleration when available.
5. Click the Firefox menu and select Exit.Click the Firefox menu at the top of the screen and select Quit Firefox.Click the Firefox menu and select Quit.
6. Start Firefox the way you normally do.