I'm running Arch Linux, latest Chromium doesn't seem to accept extension installations:

How should I work it out ?
Please look at this: Chrome Fix: Extensions, apps, and user scripts cannot be installed from this web site. To quote from there:
A workaround has been created, but it is not pretty. To bypass the protection, you need to download the extension or userscript to the local system. Once there, you need to drag and drop it into the chrome://chrome/extensions/ page in the browser. If you drag and drop it elsewhere, nothing will happen.
Please note that the author of the article covers MS Windows and this may not be applicable to your OS.
Another solution offered by the author is to include the following switch to the browser command:
--enable-easy-off-store-extension-install.
I don't know anything about Arch, but on Ubuntu 12.04, I use Gnome's Alacarte to modify the command line. (It most likely is a legitimate switch because it's available from a Googler's site. )