Ctrl + A, C, V and F don't work on Google Docs to select, copy and paste text or find text in the page; instead, the relevant key is just typed (so Ctrl + A just types A). On Facebook, when typing into a status text field, pressing Ctrl + A results in *both* the letter A being typed, and also the text *before* the newly typed A being selected. I suspect this is JavaScript related, because normal text boxes work fine (such as this bug report's box, or Google's search box). Google Docs and Facebook clearly have some code running that checks what I'm typing, that is probably overriding normal control function behaviour. However, I don't experience this issue on Google Docs with Chromium (haven't tested Facebook). I tried restarting in safe mode with addons disabled and the problem did not go away. In case it helps, I have applied the following about:config settings in addition to those set via layperson-accessible settings menus etc.: media.autoplay.enabled = false dom.webnotifications.enabled = false privacy.firstparty.isolate = true privacy.resistFingerprinting = true browser.send_pings = false Unfortunately I've not been running Firefox Nightly for long - only a few days as I just set this computer up - so I can't tell for how long this problem has been there. At least on Firefox 57 I did not experience this issue.