Comment 6 for bug 1772430

Description:
When Paragraph style - line spacing - proportional is set to value smaller than 100%, the spacing between first and the second line in the paragraph is wrong, it is too small. The second line ends up being too close to the first line. It looks very odd.

It gets worse is you set "line spacing"- proportional to really small values, like 60% or 50%.

Other lines in a paragraph seem to be spaced correctly.

All fonts are affected, but on some fonts the error is less noticable.
With "liberation serif", the error is smaller.

Try "Deja Vu Sans", line height: proportional-57%
Try "liberation serif", line height: proportional-50%

On some fonts, like "Charis Sil", it gets really annoying at proportional-90%

Steps to Reproduce:
1. Type a paragraph of text having at least 3 lines, (5 is better)
2. Change the font of the paragraph to "liberation serif"
3. Right click on the paragraph, select "edit style", go to "Indents and spacing", "Line spacing", set it to "Proportional":50%, click OK

Actual Results:
The spacing between the first and the second line is smaller than spacing between second and third line.

Expected Results:
All lines spaced evenly.

Reproducible: Always

User Profile Reset: No

Additional Info:
There is an additional bug. When line spacing: proportional is set to small values (<40%), the (rendering of) first line of text get clipped on it's upper part.

User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:49.0) Gecko/20100101 Firefox/49.0