Issue
1

Iceweasel 29 introduced the Australis UI bearing an "ALT" shortcut to
display the full menu bar. This feature conflicts with "ALT" being used
as a modifier in many Window Managers (i3/etc) and can be annoying for
the user. Feature can be disabled by default and the menu bar can be
enabled by "right click > Menu Bar".

Work Around :

set "ui.key.menuAccessKeyFocuses" from "True" to "False"

Issue 2

Visiting a website with swf content without having any swfplayer plugin
installed displays "Install (Flash)". The default
"plugins.notifyMissingFlash;false" to disable the notification isn't
effective and hence the string can be changed to something like "Install
(swfplayer)".