This may be a little off-topic but here goes..
Right. You're web browsing with Firefox. You've decided you want
that ebook. You know, the one you've been eyeing for a while.

There are two situations:
1) You get a bland link to a URLLINK.acsm file.
You click on it, it pops up a window asking you to save the file or open it with another app. It defaults to Digital Editions. Since I want to open it with Sony Reader software, I look in the little popup, but no Sony Reader mentioned.
You're forced to save it. Windows doesn't have a default file type for a .acsm file, so you'll forced to run the Sony Reader software and 'drag and drop' the acsm file to download your ebook.
Or worse yet, you anticipate, plug in your Sony Reader and both Digital Editions *and* Sony Reader software launch automatically, cluttering up your screen and generally bebothering you.
2) You get to click on a little button in a Flash program that promises to download your ebook with Digital Editions. Okay, you think, but it's a pain. You click your button, it launches Digital Editions. Then Firefox pops up a window asking you to save a acsm file or open it with another app. It defaults to Digital Editions. Since I want to open it with Sony Reader software, I look in the little popup, but no Sony Reader mentioned.
You're forced to save it. Windows doesn't have a default file type for a .acsm file, so you'll forced to run the Sony Reader software and 'drag and drop' the acsm file to download your ebook.
Both scenarios make things rather sloppy from a user perspective.
I could well imagine someone without a technical mind might find things rather confusing. In terms of the original poster, sorry mate it won't work unless you can strip DRM and convert it, which may prove more confusing; best to contact the manufacturers and complain. Maybe if you complain loud enough, they'll get with the times and provide an update so you can access our pool of ebooks in formats supported by Adobe Digital Editions (i.e. the EPUB or PDF file formats) and join us reading!