Description:
Text that has both increased character spacing and ligatures will have faulty justification, caret positioning, spell-check underlining etc.

Basically, justification, caret positioning or spell-check underlining behave as if the text had no ligatures. This looks to me as if all these operations were applied before the ligatures when it should really be the other way around.

Steps to Reproduce:
1. Type text with potential ligatures (like "fi" etc.)
2. Choose a font with these ligatures (e.g. "FreeSerif" or "Linux Libertine").
3. Increase character spacing ("Character..." dialog, "Position" tab, positive value in "Spacing", e.g. "5.0 pt")
4. Make sure that the ligatures are still displayed if necessary (e.g. by using a zero-width joiner or by explicitly setting "FreeSerif:liga=1")

Actual Results:  
After a word with a ligature, things are positioned further right as if the word had not been shortened by the ligature:
* The caret is further right than where new characters are typed.
* Line justification will cut off the line before it reaches full width.
* Spell-check underlinings are shifted right and take up more place than the word length.

Expected Results:
* The caret should be where new characters are typed.
* Line justification should reach full line width.
* Spell-check underlinings should be under the word.


Reproducible: Always


User Profile Reset: Yes


OpenGL enabled: Yes

Additional Info:
This bug is not about the default behaviour of ligatures when character spacing is increased. Whether or not increasing the character spacing disables ligatures (as it should, see bug 93033), we can still choose to have increased character spacing with ligatures, e.g. by setting "liga=1" or by using a zero-width joiner.


User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:57.0) Gecko/20100101 Firefox/57.0