Internet company Mozilla Corp said on Wednesday it was suspending advertising on Facebook Inc's social media platform on concerns of data privacy. The decision follows allegations that a political consultancy gained inappropriate access to data on 50 million Facebook users to build profiles on American voters that were later used to help elect U.S. President Donald Trump in 2016. "We found that its (Facebook) current default settings leave access open to a lot of data \u2013 particularly with respect to settings for third party apps," Mozilla said in a blog post. On late Wednesday, Facebook Chief Executive Mark Zuckerberg apologized for the company's handling of a row over user privacy, while promising tougher steps to restrict developers' access to such information. Mozilla said it would consider returning to Facebook if the company strengthens its default privacy settings for third party apps. British advertising group ISBA on Wednesday threatened to pull out ads for big brands if investigations show user data has been misused, the Times reported , adding that ISBA will meet Facebook executives this week.