You are using a beta version, so there may be bugs.

Are you using any 'tab' add-ons?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. A small dialog should appear. Click Start In Safe Mode (not Refresh).

Is the problem still there?

Tab switch is not working after update (Version 49.0.2) on 10/11/16 and opening in safe mode does not help! A new browser view opens but that has same fault. What is the problem and is there a solution? I shall Restore my PC to try to get back to a version that works as it did before the last update! I do have the tile Tabs add-on, so might this be the cause of the fault even though it is not being used at present? I can open a new tab and get to another website via Speed Dial add-on.

chippyal Please go to the top of any support.mozilla.org web page and use the Ask A Question link; https://support.mozilla.org/en-US/questions/new This will let us look at your system details. No Personal Information Is Collected.

Your email reply and that one above is just sending me round in circles. my question is above and you have responded to it. I have followed your instructions and have got back here. please give me a solution. The situation has got worse because having undertaken a Restore back to yesterday I cannot now open Firefox from the icon on my Taskbar! When trying to open Firefox a window opens stating "Couldn't load XPCOM". I may have to try to download a new copy of Firefox! I am running Windows 10 and had Firefox operating with an option to use the "tab tile" add-on, although this was not being used at the time the tab switch fault occurred.