I'm having a lot of problems with browsers crashing on many sites.
It is happening with Firefox, Galeon and Epiphany and I get this message in the terminal -
The program 'Gecko' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
(Details: serial 99 error_code 8 request_code 146 minor_code 3)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the --sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)

Here are two url's which crash all three above browsers every time without fail -
http://www.zedge.no/?side=sitemap&s=ti
http://www.myforum.lasyk.net/showthread.php?t=7839
There are many others causing the crashes but the above two are the only ones I can recall at the moment.

I don't have these problems if I visit the sites in Konqueror.
I'm afraid I can't pinpoint exactly when this started happening but I'm assuming it is after some upgrade or other.

FWIW: WinXP SP2, Firefox 1.0.2, I get a Norton Internet Security ActiveX alert, a cookie request, and a fine load of the page.

no crash here.
iirc those browsers all share the same set of libraries.you may want to try a fresh install of ff/mozilla to see if it clears things up.

I eventually discovered that by removing the flash plugins from the Firefox plugins folder, it no longer crashes. However I cannot work out how to disable flash in Galeon (I'm not bothered about Epiphany since I don't use it and have now removed it).
Can anyone tell me how?
Also, would removing flash from my Linux altogether have any adverse affect on anything?

Look into /etc/X11/xorg.conf, go to Extension section and disable "composite" or comment the line.
I fixed it doing that.
Regards
subzero.