Skip "testDragDropOntoHiddenItself" test on Selenium 2 + Firefox

[aik099]

Closes #391

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.20%. Comparing base (867a928) to head (d9ab42a).
Report is 29 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #401      +/-   ##
============================================
- Coverage     90.52%   86.20%   -4.32%     
- Complexity      180      193      +13     
============================================
  Files             1        1              
  Lines           517      551      +34     
============================================
+ Hits            468      475       +7     
- Misses           49       76      +27     

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[uuf6429]

Other than the two minor comments I left, what about that failing build? I haven't investigated it, but at first look it doesn't sound random.

[uuf6429]

Other than the failing test, this looks fine to me.