Currently in Jira, the autocomplete dropdown dialogs are limited to the triggering field's width.

This makes sense from a UI perspective, but often values have a long common prefix, posing a challenge to users and Admins to select and manage the appropriate options.

If admins could be allowed to configure a max-width for the dropdowns that'd exceed the triggering field's width, it'd be appreciated.

This is also observable in Assets/Insight, specially on some quick edit dialogs that further narrow all fields' width.

Workaround

The only workaround known is forcing the width through a custom stylesheet injected through the Announcement Banner.

This has a system-wide effect and should only be used as a last resort, should the benefit of increasing the autocomplete dialog width surpass the awkwardness of having a wider-than-expected autocomplete dialog width on other screens.

<style type="text/css">
  .ajs-layer.box-shadow.active {
    width: 500px !important;
  }
</style>

You may change the value 500 for another that works best for your scenario.

This is an example of how the workaround above would look in an Assets edition screen:

 

Assets (Jira Service Management)

Assets (formerly Insight app, now bundled with Jira Service Management) is even strongly impacted by this as Object fields all work as autocomplete, and in some screens the width of all fields are considerably reduced to fit in the dialog.
The same workaround above works in Assets.