Readium seems to work pretty well for ePub not protected by DRM. You can download from your Cloud storage solutions then open in Readium, or, if you know the URL to the file you can open it directly in Readium.
Also, if your ePub files are held in Google Drive then you can use ChromeOS's own file manager within Readium to open the file from the Cloud.
If your ePub files are DRM-protected, then you can read them using the web player for the particular store (assuming one exists). For example, if you bought your book from Google Play then Google's own reader works both on and offline on the Chromebook.
What we can't do (yet) on Chromebooks is download an Adobe DRM-protected book outside of the specific shop apps and open it. Adobe haven't written a version of Adobe Digital Editions for ChromeOS.
Note that on the Chromebook you'll be using the built-in Chrome browser. The three alternate browsers that you specified don't have versions for ChromeOS. However, note that Comodo is built around Chromium, so the underlying technology is presumably the same as for Chrome on the Chromebook.
Incidentally, why the thumbs down in the thread subject?
Graham