I just went to have a look at the Netsurf repository.
The download pauses for about 10-15 seconds between each update
of the number of kb downloaded, there is only about 438k but it
took a while.
Also Netsurf grabbed over 50MB of memory and when it rendered the
page it said it took 1133.4s
I tried the less complex Highwire browser and it took less than
3s for the whole thing.
I expect finding the cause(s) could be difficult.