While Ebola is supposed to have a higher fatality rate than Marburg, Marburg doesn't always play by the rules.
Marburg's fatality rate varies widely from outbreak to outbreak. The CDC says the fatality rate of Marburg outbreaks varies from 25% to 80%. The Congo outbreak from 1998-2000 had approximately a 80% fatality rate. The 2005 Marburg outbreak in Angola had almost a 95% fatality rate.
The Ebola fatality rate in Sierra Leone was just 39%.
“outbreaks vary”