470848 - moz-column-count incorrectly calculates line count on some font sizes

Status: UNCONFIRMED

(Core :: Layout: Text and Fonts, defect)

Description

[Michiel Sikma]

User-Agent:       Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-GB; rv:1.9.0.5) Gecko/2008120121 Firefox/3.0.5
Build Identifier: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-GB; rv:1.9.0.5) Gecko/2008120121 Firefox/3.0.5

When using -moz-column-count and a height, Gecko should attempt to fill out one column before moving on to the next.  That means one should be able to set a div to a height of, say, 3em with a line-height of 1.5em to get exactly 2 lines of text in a column.  This works--most of the time.  Sometimes it doesn't.  In my test case, I attempt this with a font-size of 0.77em, which causes the columns to become only 1 line in size.  Making the height 3.001em instead of 3em works around the problem.

Reproducible: Always

Steps to Reproduce:
1. Make valid HTML page containing a div with some text.
2. Change the font-size to 0.77em via CSS, add -moz-column-count: 2; height: 3em; line-height: 1.5em; to the div.
3. To see what it shold be, just turn off the font-size: 0.77em;
Actual Results:  
After step 2, I see a div with columns that contain just 1 line of text. After step 3, the div's columns have 2 lines of text.

Expected Results:  
After step 2 one should see the div's columns contain 2 lines of text. The software renders step 3 correctly.