Many have been having problems viewing the transliterations. I use the fonts URW Palladio transliteration fonts provided by Omkarananda Ashram.
Please click here to download the zip file.
Extract the file to any folder.
Go to Control Panel > Fonts (You may have to switch to classic view if you don't see the folders)
Go to File > Install New Font
In the window that opens up, go to the specific folder where you have extracted the zip file. Select all and click OK.
Now when you restart firefox you should be able to view the transliterated slokas.