added keyboard shotcut to show firetabs - F9
added icons, changed file structure, media files separated out, some refactoring/renaming
refactoring / file moving, min version switched to 4.0 instead of mistakely picked 3.6
modified build script to copy icon.png to addon root
build script: added distributable xpi checksuming
merged branch dev into master
addon version bumped to 0.3.2