Description of problem:
This is a very well known issue. Appearing and getting fixed and reappearing for long time for most of the rendering engines we use.

Rule : For All Indic Locales, any composed character should be entirely deleted with a single DELETE Key press, positioning the cursor at the left-hand side of the character.

Version-Release number of selected component (if applicable):
firefox-24.0-1.fc20

How reproducible:
Always

Steps to Reproduce:
1. Install F20 TC6 in any Indic locale
2. Find or type any composed character, specifically GSUB. Or open : http://utrrs-testing.rhcloud.com/language/te/gsub  and copy and paste any GSUB
3. Place the cursor on the left hand side of the composed character
4. Press DELETE Key once
5. Observe the result

Actual results:
Only first base character is getting deleted instead of the whole GSUB or composed character.

Expected results:
The whole composed character should get deleted with a single DELETE Key press as per the rule.

Additional info: