Slow page rendering with Firefox

[Raman Gupta]

The firefox on my fully updated Fedora Core 4 box renders many larger
pages very slowly. During the page rendering, Firefox "hangs"
completely. A good test page is:

http://scragz.com/tech/mozilla/test-rendering-time.php

Rendering the scragz page, and others, on the same hardware and OS,
various other browsers are over 4 times faster, including Firefox for
windows:

Linux Firefox 1.06                  42.23
Linux Konqueror 3.4.2-0.fc4.1       13.27
Linux Opera 8.02 build 1272          7.08
Windows (via VMWare) Firefox 1.06    8.18
Windows (via VMWare) IE 6            7.12

All of the above times are without any extensions *or* plugins installed
(in fact, with Greasemonkey installed, Linux Firefox took over 100
seconds to render).

Running an strace on the Firefox process while loading occurred shows a
lot of time being spent in brk() calls (usually one brk call was over
20s). Here is output from "vmstat 5" while the page rendering is occurring:

procs -----------memory---------- -swap- ---io--- --system-- ----cpu----
 r  b   swpd   free   buff  cache  si so  bi   bo   in    cs us sy id wa
 [...]
 0  0 620600  76896   7292 432368  0  0   1     4 2212  4947  7  5 88  0
 1  0 620600  76896   7316 432372  0  0   0    18 2213  4963  9  6 85  0
 [page load starts]
 5  0 620600  76772   7348 432624  0  0   6    66 2282  4882 64 10 25  1
 1  0 620600  76672   7364 432640  0  0   1     6 2205  4909 94  6  0  0
 3  0 620600  76648   7388 432652  0  0   2    20 2228  4943 92  7  0  0
 1  0 620600  76416   7412 432668  0  0   1    67 2217  4910 94  6  0  0
 2  0 620600  76408   7428 432684  0  0   1    18 2224  4889 93  7  0  0
 2  0 620600  76276   7436 432696  0  0   1     2 2210  4889 93  7  0  0
 1  0 620596  76260   7452 432712  1  0   2    18 2213  4871 91  9  0  0
 1  0 620596  76292   7468 432728  0  0   1    11 2213  4868 90 10  0  0
 [page load ends]
 3  0 620596  75384   7524 432756  0  0   6    26 2258  5537 69 12 19  0
 0  0 620596  75308   7540 432768  0  0   1    14 2215  4885 16  7 77  0
 0  0 620596  75144   7680 432840  0  0  12   161 2232  4957 10  8 81  1
 0  0 620596  75176   7696 432856  0  0   1    50 2213  4926  7  6 87  0

So swapping is not an issue. Lots of memory is available if cache is
included. Not much disk activity is happening, but the CPU is getting
hammered.

This was also tested using a completely new profile (no ~/.mozilla
directory present), with the same result.

Can anyone else duplicate these results?  Does anybody have any other
debugging/setup/configuration suggestions?

Cheers,
Raman Gupta