In the following video, a women asks Hillary Clinton why the US State Department staff cannot use Firefox, even though the browser is completely free and was approved for the “entire intelligence community.” The answer? Deploying and maintaining the browser is “too expensive.”
The only reason I can think of as to why they would give an answer like this is that the organization runs non-standard compliant applications that only work under IE. Converting those applications could cost a lot of money. But noting deployment and maintenance costs as reasons to not adopt the browser is completely ridiculous.