You have to change settings in the JAS.ini as well as in IE at the client. See below, taken from the Garden.
The following are the steps to turns on autocomplete for the web client
1. In the OWWEB section of the JAS.INI add the following setting:-
AutoComplete=ON
2. Auto Complete only works for Internet Explorer and two additional properties must be set. In addition to the JAS.INI setting you must go to Internet Explorer options, select the advanced tab, check the box for "use inline AutoComplete". Then on the content tab, click the AutoComplete button and check the "forms" box to ensure that this functionality will apply to fields on EnterpriseOne screens.
3. Sign in to the web client, and run any application and click the Tools icon in the upper right hand corner, and choose "Options", make sure "autocomplete" is checked.