For Studio instances that are accessed through HTTPS, Internet Explorer will issue mixed mode alerts on some FishEye and Crucible screens because it tries to load the IDE Connector image through HTTP.

The relevant FE issue is: http://jira.atlassian.com/browse/FE-1890

The workaround is to instruct customers to turn off the 'Enable IDE icons' option in their FishEye profile. This can be accessed by clicking their username in the top-right of the screen and choosing 'Profile', then 'Tools' -> 'Source Preferences' (the option is down the bottom). This is a per-user option and it appears it cannot be set globally.