am using ubuntu now. when i was using windows, firefox was my favourite browser. it used to be very fast.

but when i shifted to ubuntu, i find that firefox has gone very slow and also it crashes (hangs) very often.

is it because of some configuration mistake?

it is having problems when updating. what could be the problem?

It may be your extensions. Whenever Firefox wouldn't open for me in Linux, i would delete the extensions and "magically" Firefox opens up again. I find the extensions for Firefox in Linux a bit unstable when compared to their Windows' counterpart. Your Firefox settings should be located at
But i'm an Opera user. I only use Firefox in Linux for checking out compatibility between browsers.

Firefox being slow on Ubuntu is a known issue and has been discussed on the Ubuntu forum for a long time now. Apparently other distro"s do not have this problem with there versions of Firefox. There is also a Swiftfox version of the browser that is supposed to be quicker. I installed Swiftfox using the Automatix installer. I also read some tricks on the Ubuntu forum using about:config to tweek some of the network settings which helped a lot of users.