Yes, you can build you own personalized extension for Firefox, Chrome or Opera from PDF.js source code, which will disable text layer. (see also #textLayer=off feature at https://github.com/mozilla/pdf.js/wiki/Debugging-pdf.js#url-...)

Memory suggests yes (I think it's just a render param you pass in or something?) but I'll need to check old code tonight to give you a definitive answer.