Try the following (not guaranteed to cover your problem but it's a possibility):

Open your Dash and type in "Tweak" to get to the Tweak Tool (Note that this is not the same as "Ubuntu Tweak") - alternatively, in a console type gnome-tweak-tool (if it is not currently installed, type sudo apt-get install gnome-tweak-tool to install it)

Go to the Keyboard & Mouse > Emacs input (formerly Theme section > Gtk+ Keybinding Theme). If this is set to "Emacs", then Ctrl+A will essentially act as if it were the Home key. If this is the case, change the option to "Default" to restore the usual settings.

Alternatively, in Firefox and Google Chrome you can use the shortcut Ctrl+L to select the entire title bar.