I found an old bug for this for older versions of Windows, but by no means does this mean they should not work if they are up to unicode standards. Can you please clarify if this is a website not displaying the language properly of if its the language version of Firefox itself?

ref bug 1811880

sivaramkrishna said

Telugu fonts are not being rendered properly after upgrade. consonant and vowel ending symbols are appearing separately rather than integrated fashion, giving a very odd look for the text in Telugu

It is the language version of Firefox. Problem is only with Telugu fonts. And on all web pages where Telugu fonts are present. Other languages are displayed(Hindi, Tamil etc.) correctly.