Why don't you follow Firebird's datediff() syntax
Which would lead you to something like
SELECT DATEDIFF(MINUTE FROM CAST('2010-01-22 15:29:55.090' AS DATE) TO CAST('2010-01-22 15:30:09.153' AS DATE)) / 1000.0 AS Secs
As a side note, if you divide the number of minutes obtained by 1000, you will not get the number of seconds. If you want to get the number of seconds from the number of minutes, you have to multiply minutes by 60.
Finally, as a general rule, you should always have a look at the reference pages of the database engine you are using (i.e., Firebird). SQL language is not universal across all engines, there are some common words between all but each one also has its tiny specificities. Copy-pasting a SQL code of another engine and expecting it to work is accepting to loose at bunch of time.