spontaneously eats up all RAM after closing 'filezilla'

[LAZA]

Binary package hint: firefox-3.5

I tried to copy some file over ftp with 'filezilla' but the server couldn't connect.
So I opened another 'firefox' window und connected via http und edited password etc.
After retrying to connect with 'filezilla' and connection was refused I closed 'filezilla' and spontaneously 'firefox' eat up all my 8 GB of RAM (Firefox 15:20) and needed about 25 % of CPU power.

After several minutes the RAM is still half filled only with the 'firefox' (Firefox 15:27).

If it is of note - three windows with these sites:
- myfreefarm.de
- arcor.de / metalflirt.de
- funpic.de

ProblemType: Bug
Architecture: amd64
Date: Sat Mar 6 15:22:01 2010
DistroRelease: Ubuntu 9.10
NonfreeKernelModules: fglrx
Package: firefox-3.5 3.5.8+build1+nobinonly-0ubuntu0.9.10.1
ProcEnviron:
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-20.57-generic
SourcePackage: firefox-3.5
Uname: Linux 2.6.31-20-generic x86_64

[LAZA (laza74)]

After closing all windows and restarting 'firefox' the behaviour is back to normal:
virtueller Speicher 536 MB
nicht auslagerbarer Speicher 102 MB

RAM:
16 % program load
5 % Cache