Hi Prashant, did you test in Firefox 65? '''Firefox 65''' stopped sending the page a '''keypress''' event for non-printing keyboard combinations. If you want to intercept them, you need to look at one or both of the other key events, '''keydown''' and '''keyup'''. More details here: * https://www.fxsitecompat.com/en-CA/docs/2018/non-printable-keys-no-longer-fire-keypress-event/ This page has an example of how to intercept Ctrl+b (normally opens the Bookmarks Sidebar): https://www.jeffersonscher.com/res/keyvents.html ---- '''Firefox 66''' enabled '''window.event''' for cross-browser compatibility but this may break some scripts that do not expect Firefox to support that object. More details here: * https://www.fxsitecompat.com/en-CA/docs/2018/support-for-window-event-and-event-returnvalue-has-been-added-again/ If you can find where your code relies on the old behavior, hopefully you can update that to work with ''both'' Firefox's legacy behavior (to support Extended Support Release users) and its new behavior. Meanwhile, this has broken some big name applications, so Firefox has an exceptions list. It's not very practical for you to explain to your users how to use that, but I'll describe it anyway in case you see a way to use it: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk. (2) In the search box above the list, type or paste '''hack''' and pause while the list is filtered (3) The '''dom.keyboardevent.keypress.hack.use_legacy_keycode_and_charcode''' preference lists servers on which Firefox will send scripts in the page older style keyboard events. To add your own server, double click this preference, add the host name at the beginning followed by a comma (no extra space) and click OK.