Today I noticed that when you click on Torbutton with the left mouse button instead of starting the TOR support, a menu pops up - the same menu that you usually see when you click with the right mouse button.
It turns out that Torbutton has updated itself two days earlier and this is a bug (or a feature?) of the new version.
Since I don't like it this way, I decided to change it to the way it was before the update.

Depending on your Firefox installtion on Windows, you can find the its extensions here:
C:\Documents and Settings\<user>\Application Data\Mozilla\Firefox\Profiles\<random>.default\extensions
or here:
C:\Program Files\Mozilla Firefox\extensions

The source code is located at {e0204bd5-9d31-402b-a99d-a6aa8ffebdca}.xpi (which is a regular zip archive that you can rename from xpi to zip and unzip it with a regular zip manager), and the file that you need to change is chrome\content\torbutton.xul

The code that needs to be changed:

chrome\content\torbutton.xul - before<toolbarpalette id="BrowserToolbarPalette">
    <toolbarbutton 
        id="torbutton-button"
        class="toolbarbutton-1 chromeclass-toolbar-additional"
        label="Torbutton"
        tooltiptext="&torbutton.button.tooltip;"
        menu="torbutton-context-menu"
        context="torbutton-context-menu"/>
</toolbarpalette>

needs to look like this:

chrome\content\torbutton.xul - after<toolbarpalette id="BrowserToolbarPalette">
    <toolbarbutton 
        id="torbutton-button"
        class="toolbarbutton-1 chromeclass-toolbar-additional"
        label="Torbutton"
        tooltiptext="&torbutton.button.tooltip;"
        oncommand="torbutton_toggle(true);"   <!-- HERE //-->
        context="torbutton-context-menu"/>
</toolbarpalette>

After that you can archive everything back with zip and change the name to {e0204bd5-9d31-402b-a99d-a6aa8ffebdca}.xpi OR to put everything in a directory named {e0204bd5-9d31-402b-a99d-a6aa8ffebdca}.

Congratulations, Torbutton is now working as it should!