firefox:

strace -c -p 2819
Process 2819 attached - interrupt to quit
Process 2819 detached
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
100.00    0.000012           0      5262           gettimeofday
  0.00    0.000000           0       214           read
  0.00    0.000000           0       160           write
  0.00    0.000000           0      3901           ioctl
  0.00    0.000000           0      1963           poll
------ ----------- ----------- --------- --------- ----------------
100.00    0.000012                 11500           total


opera:

strace -c -p 7030
Process 7030 attached - interrupt to quit
Process 7030 detached
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 89.56    0.001998          24        85           select
 10.44    0.000233           0       672           read
  0.00    0.000000           0       672           write
  0.00    0.000000           0        13           time
  0.00    0.000000           0        85           ioctl
  0.00    0.000000           0       816           gettimeofday
------ ----------- ----------- --------- --------- ----------------
100.00    0.002231                  2343           total