I believe this is raised in the OpenQA Jira: http://jira.openqa.org/browse/SIDE-316. It has also been discussed here: http://clearspace.openqa.org/message/64455
Until the issue has been resolved you can revert to the 1.0b2 version of Selenium IDE http://release.seleniumhq.org/selenium-ide/1.0-beta-2/ but this wont install on Firefox 3.5.x unless you disable extensions.checkCompatability in about:config. See http://kb.mozillazine.org/Extensions.checkCompatibility