This might be related to Firefox randomly disables keyboard input, Keyboard input is not working in Firefox ALONE and keyboard input only works in the most recently created window.
When Opening several Firefox windows (for this discussion I will talk about 2 windows A and B, each with several tabs), occasionally the keyboard input is stuck on one of the Firefox window (lets say A).
Clicking window B brings it into focus, and I can use the mouse to scroll and move between tabs, but every keyboard input (either in any of the tabs, or in the url or search bar) is not sent to window B. Instead the input is still sent to window A (wherever the cursor was in window A before it lost the focus).
- If I drag a tab from window B into window A, I can interact with that tab in window A.
- If I kill the Firefox process and restart it (restoring sessions), the problem goes away, until it for unknown reason comes back.
- If I move a tab to a new window C from B, then both C and A gets keyboard input but not B. If I join that tab back to B, now B gets keyboard input, but not A.
No other application suffers from this issue.
My environment is Ubuntu 14.04 with KDE 4.13.3.
I am on an up-to-date version of Firefox (currently 57.0) but I have seen this issue on older versions too.
Edit:
Inspired by @harrymc's comment, here is my extension list:
- uBlock Origin 1.14.18 by Raymond Hill
- Valence 0.3.8 by Mozilla
and my plugin list:
- OpenH264 Video Codec provided by Cisco Systems 1.7.1
- Adobe Flash 27.0.0.187