Notably, their code for their Firefox extension^1, while not free software, is available to look at. Firefox extensions are delivered as an XPI file (https://de

Notably, their code for their Firefox extension^1, while not free software, is available to look at. Firefox extensions are delivered as an XPI file (https://developer.mozilla.org/en-US/docs/XPI https://developer.mozilla.org/en-US/docs/XPI), which is simply a renamed .zip . So it can be extracted with gunzip, 7-zip, winzip, etc. Inside the .xpi are various human-readable files, including .js, .xml, and .config files (https://developer.mozilla.org/en-US/docs/Bundles https://developer.mozilla.org/en-US/docs/Bundles). So you can literally examine the source of any Firefox extension. And not just source you hope is the same as the delivered extension^2, but literally the running code. So no, it's not free software. But it is accessible for you to read^3. [1] I _know_ this is true for Firefox. I think it is for Chrome, but I'm not sure. I have no idea for any other browser. [2] How do you know the code for e.g. Firefox that you clone from https://hg.mozilla.org/mozilla-central/ https://hg.mozilla.org/mozilla-central/ is the same code used to build the browser downloaded at mozilla.org ? You don't, unless you go to the lengths of building it yourself and doing a bitwise comparison of the executables, but that is going to be error-prone. But you can pull the Lastpass extension out of your profile and see the exact code being run. [3] Unless they download code from somewhere and eval() it.