EPUBReader is a Firefox addon which lets you read ePub-files just in the browser. You don't need to install additional software!
If you click on a link to an ePub-file, you are normally prompted by the Firefox "save as" dialog. With EPUBReader installed, the ePub-file is downloaded, processed and directly displayed ready to read.
It runs on every operating system Firefox does (Windows, MacOS X, Linux) and is already used by more than 400,000 daily users.
EPUBReader is available in 23 different languages: Catalan, Danish, Dutch, English, Esperanto, Finnish, French, German, Greek, Hebrew, Hungarian, Italian, Japanese, Lithuanian, Polish, Portuguese (Brazilian), Portuguese (European), Russian, Simplified Chinese, Spanish, Swedish, Traditional Chinese, Turkish.
“This extension is so excellent I actually installed Firefox 3 to get it (and I really dislike Firefox 3).” Addons.mozilla.org