If you can't login to an Intuit website (e.g. to buy Turbotax), the problem could be that you have disabled "DOM storage" in your browser.
A typical symptom of this issue is that a spinning wheel appears and the site refuses to do anything else.
To attempt to fix the issue in Firefox, use about:config and examine the setting "dom.storage.enabled" (without quotes). If it is "false", double-click it to set it to "true" and refresh the page.
Note that it is best -- for security and privacy -- to leave this setting disabled, but that breaks some sites.