There is an unexpected javascript error with Activity Stream gadget on IE8.

Workaround

Downgrade the Activity Stream bundled plugin to 5.3.25 version following these steps:

1. Back up everything beforehand. Please be advised that we can't guarantee any further support if something wrong happens because of this.
2. Stop JIRA.
3. Locate and move the file JIRA_Install/atlassian-jira/WEB-INF/classes/atlassian-bundled-plugins.zip to somewhere else.
4. Extract the file to a folder and remove all the .jar files starting with streams.
5. Download activity stream 5.3.25.zip and extract it to the same folder.
6. Compress a new atlassian-bundled-plugins.zip from here and put it back to JIRA_Install/atlassian-jira/WEB-INF/classes.
7. Start JIRA.

In case this is not working as expected, please reuse the original atlassian-bundled-plugins.zip.