Cannot use the address bar.It shows me a problem

[paranoid_gr]

when i put a link in the address bar then i throws me an error which says "assertion failed" and then below that it says

ASSERT: *** Search: _installLocation: engine has no file!
Stack Trace:
0:ENSURE_WARN(false,_installLocation: engine has no file!,2147500037)
1:()
2:()
3:()
4:epsGetAttr([object Object],alias)
5:()
6:SRCH_SVC_getEngineByAlias(https://bugs.launchpad.net/ubuntu/+source/firefox-3.0/+filebug/9gCQTXXez4ujcwvg9HumXJxo4wv#form-start)
7:getEngineByAlias(https://bugs.launchpad.net/ubuntu/+source/firefox-3.0/+filebug/9gCQTXXez4ujcwvg9HumXJxo4wv#form-start)
8:getShortcutOrURI(https://bugs.launchpad.net/ubuntu/+source/firefox-3.0/+filebug/9gCQTXXez4ujcwvg9HumXJxo4wv#form-start,[object Object])
9:canonizeUrl([object KeyboardEvent],[object Object])
10:handleURLBarCommand([object KeyboardEvent])
11:anonymous(textentered,[object KeyboardEvent])
12:fireEvent(textentered,[object KeyboardEvent])
13:onTextEntered()
14:handleEnter(false)
15:onKeyPress([object KeyboardEvent])
16:onxblkeypress([object KeyboardEvent])

Please help me!!!My OS is Linux Ubuntu

ProblemType: Bug
Architecture: i386
DistroRelease: Ubuntu 8.10
NonfreeKernelModules: nvidia
Package: firefox-3.0 3.0.5+nobinonly-0ubuntu0.8.10.1
ProcEnviron:
 PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: firefox-3.0
Uname: Linux 2.6.27-7-generic i686