Created attachment 764573 [details] Lohit-Devanagari-W8-FF.png User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:21.0) Gecko/20100101 Firefox/21.0 (Beta/Release) Build ID: 20130516142033 Steps to reproduce: Version of components used for testing: Windows 8 Firefox 21 Steps: 1. Install Lohit Devanagari font in Windows 8 from https://fedorahosted.org/releases/l/o/lohit/lohit-ttf-20130130.tar.gz 2. Open http://pravins.fedorapeople.org/lang-feature-testing/Lohit-test.html Observe the rendering Actual results: Actual results http://pravins.fedorapeople.org/lang-feature-testing/Lohit-Devanagari-W8-FF.png Expected results: Expected results http://pravins.fedorapeople.org/lang-feature-testing/Lohit-Devanagari-W8-IE.png Lohit font has language specific rules define. When one write text by specifying lang attribute particular Open Type tables should get executed Firefox give expected results on Fedora 18 but it fails on Windows.
There is a similar bug: bug 474182
That's different: bug 474182 is about font selection, whereas this is about language-specific shaping behavior. Currently, we use Uniscribe or DirectWrite for Indic script shaping on Windows, and we do not support language-specific features via those engines. If you set gfx.font_rendering.harfbuzz.scripts to -1 in about:config, then all text will be shaped via HarfBuzz, and language-specific features should work. This is not yet the default setting because we want more extensive testing before making that switch, but it is intended to completely replace the Uniscribe and DirectWrite shaping code in the future (bug 797405).