The cube icon is not visible although the addon installs without an error and is correctly listed in the addons dialog.
Customizing the toolbar does not help either.
It seems others have/had this problem too:
https://github.com/blockchain/My-Wallet-Firefox-Extension/issues/1
https://addons.mozilla.org/en-US/firefox/addon/my-wallet/reviews/482352/
http://www.reddit.com/r/Bitcoin/comments/17fs03/blockchaininfo_firefox_extension_now_available/c852tq1
Noticed the update to v1.98 but unfortunately the addon is still not working under linux firefox.
The icon is appearing now, but clicking on it does nothing.
Opening the url (resource://jid0-3vnsclfrwladqlsm1xgb50oxar0-at-jetpack/blockchain/data/en.html) manually does open the site but freeze at "Changing Wallet Identifier".
So it doesn't work for me under linux. Any others with that problem?
Under win7 I doesn't have these issues.