Something was  wrong with database file.fdb , even after gbak restore. I deleted file for FB 3.X and recreate new database with FB 3.0.2. Now times are similar to FB 2.5.  FB_3.0.2 seems to be slighty faster than 3.0.1.

now:
//3.0.1

SQL> select count(*) from t1;

PLAN (T1 NATURAL)
Current memory = 36156184
Delta memory = 251424
Max memory = 36238024
Elapsed time= 4.984 sec
Buffers = 2048
Reads = 37895
Writes = 0
Fetches = 20076012
SQL> select first 1000000 * from t1 order by id DESC;

PLAN SORT (T1 NATURAL)
Current memory = 36156888
Delta memory = 704
Max memory = 99079336
Elapsed time= 26.512 sec
Buffers = 2048
Reads = 37872
Writes = 0
Fetches = 20075727

//3.0.2

PLAN (T1 NATURAL)
Current memory = 36252536
Delta memory = 251424
Max memory = 36334376
Elapsed time= 3.885 sec
Buffers = 2048
Reads = 37895
Writes = 1
Fetches = 10151660
SQL> select first 1000000 * from t1 order by id DESC;

PLAN SORT (T1 NATURAL)
Current memory = 36253240
Delta memory = 704
Max memory = 99175688
Elapsed time= 23.772 sec
Buffers = 2048
Reads = 37872
Writes = 0
Fetches = 10151434
SQL>