When adding multiple margin settings in rows along with IDs per row on a single page causes Firefox to crash on both Mac and PCs. The pages attempt to load but cause FF to lock up and I cannot generate a crash report to further investigate. This has been tested on multiple machines and different versions of FF on both Mac and PC.
Current versions WP 4.5.3 VC 4.12
The setup was intended to use a scroll to ID via a href. The additional settings for rows were only Margin Top and Bottom. I reverted back to the twentyfifteen theme and only turned on Visual composer to determine if the issue was related. During this test FF again locked up. I have been able to resolve the issue by setting custom classes for row margins while still using Row IDs (this was a lucky stumble upon to resolve the issue).