Add warning to Customizer about Firefox bug; refs #15016

[skip sauce]
Merge pull request #15395 from twbs/firefox-customizer-warning

Add warning to Customizer about Firefox bug
group Safari browser bugs by OS
Add Wall of Browser Bugs entry for #15205

Closes #15205
Merge pull request #15407 from twbs/close-15205

Add Wall of Browser Bugs entry for #15205
Add Wall of Browser Bugs entry for #11266, #13098

[skip sauce]
Merge pull request #15415 from twbs/webkit-bug-139848

Add Wall of Browser Bugs entry for #11266, #13098
fix "propertes" typos in comments
automatic grunt dist