Case sensitivity of email-adress checking causes indicator icon not changing the color

My work's E-Mail-server (Microsoft Exchange) automatically changes the first letters of a recipient e-mail-address of the kind <email address hidden> to uppercase:

<email address hidden> -> <email address hidden>

If the E-Mail-account E-Mail-address in Thunderbird is configured as only-lowercase, the messagingmenu extension doesn't recognize every incoming email as "directly addressed to us", because it checks the recipient address and the account-configuration address using a case sensitive matching.

This could be fixed using two different approaches:

- let the user change the thunderbird configuration according to the exchange server behaviour (i.e. first letters to upper case)
- change the messagingmenu extension code to convert the email-adresses to lower case only before checking