hello, windows system restore won't restore the file that holds the firefox history unfortunately (it is called places.sqlite). you'd need a backup of your firefox profile folder to get back this kind of data.

please also update firefox - the version you're currently using is outdated and affected by numerous security vulnerabilities.

Update Firefox to the latest release

Thanks for the reply.

Will updating to the latest version of Firefox affect my current computer history? I don't want to lose any more stuff before I have a chance to back it up. Sorry if this is a bit of an ignorant question.

no, updating the browser won't have an impact on your history - all your personal data will remain.

a general tip if you want to avoid data loss/highly depend on this data, is to back-up your firefox profile regularly: Back up and restore information in Firefox profiles

OK, thanks again!

There was something else I was wondering; how do I know whether the newest version of Firefox is compatible with XP?

it is ;-)

https://www.mozilla.org/firefox/19.0/system-requirements/

What if I'm currently using a macbook os x version 10.7.5? Not windows.. I accidentally clicked on "forget this site" button and I want to restore the site I deleted :/ Thanks in advance