In any browser, you can use the following alternative installation instead of an addon or extension. You may install GmailTeX as a javascript program in your own web directory, and start it as needed by using a bookmarklet, like so:

  1. Download gmailtex.txt and save it as gmailtex.js in some location on the Internet that you can call from your browser. Let me assume that the new location of the script is http://example.org/gmailtex.js

    Note: you can use your friends' installation if you know the web address where they put it, or the location where your system administrator installed it. But it has to be on the Internet. Neither Firefox, nor Chrome would load JavaScript directly from the hard drive for security reasons.

  2. Drag the following link to your bookmark toolbar to create a bookmark: GmailTeX.

    Alternatively, you can manually create a bookmark with the following location as one long string, without breaks or spaces (shown here as several lines only for readability):

    javascript:(function(){var%20s=document.createElement("script");
    s.type="text/javascript";s.src="http://example.org/gmailtex.js";
    document.getElementsByClassName("vI8oZc")[0].appendChild(s);})();

  3. Edit the location of the newly created bookmar and replace http://example.org/gmailtex.js by the actual location, from Step 1 above.

That should be it.