It's likely an issue with buggy video drivers. Firefox has a database of drivers on a blacklist that will crash due to instability. When it detects them in use, it will disable hardware acceleration which decreases performance and quality of some things like font rendering. Judging by the earlier screenshot, this is on a lower end laptop at 1366x768 resolution with an integrated graphics card. Most laptop makers never update the bundled drivers to fix bugs even though Intel and AMD regularly update the drivers of their integrated graphics tech. So, users are stuck with an outdated buggy driver and no way to update it. Mozilla at least ensures that it won't crash.
My screenshot is from a PC with AMD A10-7850K with integrated Radeon R7 graphics. I always download the latest AMD drivers and check for updates every month.