When installing Adblock Plus in Firefox for Android, it currently tries to pop up a XUL settings page on first run. This hasn't been supported on Android for over a year now, and (due to a bug in Firefox) locks up the browser.
We'll fix the Firefox bug (https://bugzilla.mozilla.org/show_bug.cgi?id=947162), but it would be nice if Adblock wouldn't try to show a XUL plugin UI on mobile.
After first run, the issue no longer presents because Adblock Plus does seem to support the normal non-XUL add-on configuration UI in Firefox for Android.