^^ This made no sense.
Assuming you mean install a browser on a USB stick then open it in school and you can browse the net there are several flaws:
One, you cannot drag and drop a browser onto a USB stick, unless you mean a portable browser edition, in which case you need to download then install it to the stick.
Two, any school will block that in one of two ways, where I work (a school in the UK) we have an internal proxy, if you bypass that proxy you get NOTHING. There is no way around this, there is no back door. If you dont go through our proxy you can NEVER connect to the internet, no matter what you try. OUR proxy is the ONLY connection to the net. So if you got your own browser onto the system and put it a web proxy from the net (ie one of the annonymising sites) you just wouldnt get any net. The other option for blocking it is simply to block the firefox, opera, chrome etc... programs from running via a policy (on a windoze network) You can get around that by renaming your firefox etc... to "iexplore.exe" but even that is easy to block by telling the policy to only allow IEXPLORE from the correct windows directory, which of course you dont have write access to and thus you cant do it.
Assuming the target network has no internal proxy the best option is to run up a live CD of ubuntu