BuddyPress.org

This is a heavily customised theme. Generally the support forum here helps with matters related to the running of BuddyPress and the BuddyPress default theme.

Although it almost certainly an issue with the themes styling to determine that absolutely one should drop back to the BP default theme to check if the issue still persists.

Fixing styling issues with third party themes is slightly beyond the remit of this forum but someone may take a look for you and offer some suggestions (presently I am without the two aforementioned afflicted browsers)