i joined the forum specifically to help with this. i've been looking for a solution on all the olpc/xo/sugar forums i could find, and i haven't found the answer.
i have found a solution- at least to cookies, which i'm sure could be adapted to history. the only reason the solution is not in this post is i haven't posted here before, and though i'm sure the xo / sugar is an environment that is literally made to be tinkered with, i'm not sure how many "tinker" posts are welcome here. i'll continue to look around the forum and try to find a baseline. note there is an "xo hacks" forum at olpcnews and i would be happy to answer this question there, since it's clearly there for such answers.
i will tell you what did not work and what i have not tried. i was unable to install any mozilla addons for the browser in sugar. it simply doesn't want to use them. if i was sure what browser was being used (i should try about: to see for sure) i might have a good idea why not.
i tried setting cookie duration from 90 days to 1 day. i am not sure this had any effect, it has not been 1 day since i tried it. since then i have found a solution, which means that my 1 day solution remains untested. (do the cookies go away after 24 hours? i don't know. but if that works it's a very easy fix.)
i have thought about installing firefox to see if this gives me control of cookies (and if it allows me to use tabs in sugar!) right now i've downloaded ff 3.5.x but i haven't installed it. deleting cookies from there if possible) may delete them in the sugar browser also, it may not. i have tried to use ctrl-shift-del (the windows shortcut to bring up the clear recent history window) and this was unfruitful. if you come back and read this, i'd like to help if possible. i don't mean to tease with "i have the answer!" i'd like the opportunity to tell you. if a mod explains his feelings on the matter i can reply even sooner.
teachers that continue teaching should be expected to continue learning; it's an absurdity to have 19th century expectations of 21st century educators. granted they shouldn't have their time wasted (more than students,) or be paid insulting salary.