Run the test(s):

test

Instructions:

Follow these instructions after the test page opens.
The number of conjuncts supported by a font may be different from another font, so set the font to a specific value.
Identify the clusters that are presented by the font using a conjunct (ie. with a hidden virama) – these are the ones we are testing. (You can highlight some or all of these by clicking on them.)
From the pulldown labelled "Run a test" choose "First-letter".
Check the results.
Test passes if no conjuncts are only partially selected (coloured blue) and enlarged.

Results:

• Gecko: ✅❌ Most of the half-form conjuncts fail, and are broken into an initial consonant with visible virama and a following consonant. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:95.0) Gecko/20100101 Firefox/95.0
• Blink: ✅ All conjuncts are fully selected. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36
• Webkit: ✅ All conjuncts are fully selected. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.2 Safari/605.1.15

Related tests: Styling initials

Note: #68 tests the other clusters with the visible virama.