Misc: Drop support for older browsers; update support comments

That includes IE<8, Opera 12.x, Firefox<29, Safari<6.0 and some hacks
for old Blackberry.

Fixes gh-1836
Fixes gh-1701
Refs gh-1815
Refs gh-1820
Only IE<9 evaluate this code so it's here only to support these versions. Even though the code is the same as what's in line 63, I think this should say `IE<9` here.