The letter combination ffi should be turned automatically into the ffi ligature, which does not happen with version 2.34 of the font.
I tested with these applications:
LibreOffice Writer 18.104.22.168
It works fine for DejaVu Sans.
Steps to reproduce:
* In LibreOffice Writer, select DejaVu Serif (24pt to see the effect clearly)
* Type “official”
You will see that the ff ligature gets applied, but the i stays extra.
I encountered this same problem in ConTeXt, and originally reported here
I solved the problem by editing the font as such
On my mac I open DejaVuSerif.sft with FontForge
From menu select Element > Font info
From side bar select Lookups
Select 'liga' Standard Ligatures - Without dotless i
click [UP] button to move it above 'liga' Standard Ligatures
And compile the font.
copied the font to
and now ffi ligatures work.
This was needed for all 8 DejaVuSerif* fonts.