Lets say you have jira_user_A who has the Manage Watchers permission in project_A, but does not have the Browse Users global permission.

jira_user_A can still add a watcher to issues by way of typing the user's username in full, and pressing enter, although he does not get auto-suggestions, as expected, because he does not have Browse Users global permission.

This does not work for Internet Explorer 8. In IE8 you are unable to press enter (it does nothing) and the following error is seen: IE8.jpg. It is also broken if you have the Browse Users permission, but in this case you can atleast click on the auto-suggestions to add users.

In Chrome, it works just fine: Chrome1.jpg

Workaround

You can still edit the watchers list by using the Manage Watchers page instead. Alternatively, you can use more recent versions of Internet Explorer or any of the other supported browsers.