when I type inside the search bar in Youtube or Google, the letters typed are not displayed although the characters are being recognised by the engine and produce autocomplete results that are visible. I did download a fresh copy of ff via sudo apt-get firefox reinstall as suggested but this unfortunately did not work. The search pane for Google in the top most header to the left address bar does in fact show the characters as bold. with firefox in safe mode, the problem is corrected
Apparently re-installing doesn't help
run firefox from the terminal in safe mode and see if the issue remains.
If it works in safe mode, some plugin might be responsible for the voodoo
If you have addons disable them one by one to determine which one is causing it. If you have no addons installed, I'm out of ideas.