DataFox 1.9.2 adds support for the modifications made to the data.bsnl.in site a month or two ago. Support for the selfcare sites is not available in this version, I need selfcare site credentials (please email me). This version will also work with Firefox 4 beta 1.
Unfortunately, there were two issues in DataFox 1.9.1 released to earlier today; there was a data unit problem where a gigabyte value was incorrectly assumed as a megabyte value (if only BSNL really did that when calculating usage ;)) and I accidentally removed the DataFox update URL from version 1.9.1. Any users who updated to 1.9.1 will not receive any update notifications :(. If you did not install 1.9.1, you should see an update for 1.9.2 via the regular update mechanism, if you did install 1.9.1, simply go to the DataFox page and manually install version 1.9.2 to fix the problem (you will see subsequent updates as well).
Also, for users clamoring for Chrome support, DataFox for Chrome has been available for a couple of months now and includes this fix.