Ubuntu – the terminal command for launching a web app

The Chrome extension, Clutter Free, does exactly what you asked:

• switches to already open duplicate tab, when a new one is opened,
• works on redirects as long as the final redirected url is already open

Disclaimer: I'm the author for this extension. I too was looking for this solution, and ended up making the extension.

In case you want to retry adding the Gmail Unity webapp from firefox: execute sudo apt-get purge unity-webapps-gmail, restart firefox and surf to https://gmail.com. You should see the dialog asking to install the gmail webapp.

I'm experiencing the same issue, one thing I've noticed is that the file ~/.local/share/applications/GMailmailgooglecom.desktop was missing on my system. I created it and populated it with (you can create it by running unity-webapps-desktop-file /usr/share/unity-webapps/userscripts/unity-webapps-gmail/manifest.json in ~/.local/share/applications):

[Desktop Entry]
Name=GMail
Type=Application
Icon=GMail-mail.google.com
MimeType=
Actions=S0;S1;S2;S3;S4;S5;S6;S7;S8;S9;S10;
Exec=unity-webapps-runner -n 'R01haWwA' -d 'mail.google.com' %u

I also added a row for the GMail app to the applications table in ~/.local/share/unity-webapps/apps2.db and checked that the necessary values are present in dconf-editor (as suggested by sorgel).

After restarting unity I do have a GMail icon on my Unity launcher and the messages menu, the icon itself however is displayed as a question mark. Clicking the question mark in the launcher always opens a new firefox window (i.e. it doesn't switch to an existing tab if present); also the number of unread mails isn't displayed either.

So for me the webapp basically doesn't work. The Facebook, twitter and Youtube webapps do seem to be operating as expected. Filing a bug report would probably be the next step.