No mouse, can't send control keys

[whairst]

I'm on a Win7 computer, using Firefox 48 to use the WebConnector to connect to a CentOS computer. I successfully connected and logged in (which required one mouse click+drag). I can't see the remote cursor (even with "Show remote cursor" checked), and while I can type (tested using the chat window), I can't send any control keys (Alt, Ctrl, Windows key, etc). The Actions menu has Ctrl+Alt+Del (grayed out), Remote reboot (with all options grayed out), Disable remote input (not checked), and Show black screen (grayed out). At this point, I can't even log out of the remote machine, just close the local TeamViewer.

How do I get mouse control back? Is there a way to use control keys when using the web interface? (I can't install any software on the local machine, only the remote one.)

[whairst]

Yesterday evening I physically accessed the remote computer (running CentOS), and much to my surprise, it wouldn't allow me to click on most things. I suspect it's TeamViewer-related (TV 11), because sometimes clicking on other windows, it would snap back to TeamViewer instead. (TV was the only graphical software running, aside from the OS itself.) I had to reboot the machine to get it to clear. Seems to be working ok at the moment, both local and remote. Still can't send control keys through WebConnector.

I really, really want to find a way of preventing this in the future. The CentOS machine is a server, so routinely rebooting it to fix TV issues isn't an option.