It works but here are some drawbacks:
1) No drag and drop, you have to click on the extension and click on open file and only then you can open files.
2) No background page color, so if the background page color is black in the docx, it shows white
3) No page wrap option, with pdf you can have as many pages next to each other as fit on the screen.

Works well mostly. However one document I downloaded with some 1 cell tables for formatting displayed wrong in this extension (the boxes are supposed to stretch out the whole page width but in this extension they were very narrow). I tested this in the docxjs demo site and it worked correctly there. so maybe you are using an old version of docxjs? or maybe not I inspected element and both versions said td style="width: 514.8pt;", but the one in this extension did not display properly. If you could fix this that would be nice. I also noticed some other minor formatting errors sometimes

Perfectly functional while being lightweight, minimalistic and locally managed, nearly perfect addon. Works well with Moodle. Images display, support for some additional formats like .doc or .odt, and removal of the weird white margin would be great.

it works