My Manjaro is XFCE Desktop. Firefox Netflix subtitles were extremely small (unreadable). I just inserted a different desktop "Gnome" on the same Manjaro installation. It is the same Manjaro installation on the same computer but a different desktop I was playing with and I can switch between desktops. The problem disappeared with the Gnome desktop. Going back to the XFCE desktop the problem was still there. I never came across the relationship of the desktop to this problem in my readings. With Google Chrome on the XFCE the subtitles were readable. This is not a problem for me since I could use Google Chrome even though Firefox is my Browser of choice. For some things I must use Google Chrome like my US Army retired finance because Firefox is not recommended and doesn't work right. I do not like that the email address needs to be signed into to change things on Google chrome. On Firefox I just have to establish a local password. I am providing this for your information because I am able to use the computer to watch Netflix on my Manjaro XFCE setup. This information may help someone to find a solution if they are interested. I am going to have to see if there is some package that I can add to XFCE to correct the problem.