Noticable click delays in Firefox

I am using Blaze and FlowRouter. Since some weeks, I am experiencing noticable click delays in Firefox. These happen occasionally and affect all links in the app. Whereas on Chrome and mobile devices route changes are happening immediately, Firefox takes some time at random. Sometimes, the click is executed immediately, sometimes it takes about 500ms (just a gut feeling).

I used the profiler to debug this, but could not see anything special. Is there anything I could do to track down the root cause?