Bug 985598 - [email] Double-triggering of share/new activity by clicking on a mailto link results in black screen

v1.3 branch merge from master of commit c3b1f1fe0ee3e00903858333412b6de94f194629
Merge pull request #18495 from jrburke/bug985598-v1.3-email-double-activity-blank

Bug 985598 - [email] Double-triggering of share/new activity by clicking on a mailto link results in black screen r=asuth a=bajaj