Work in progress.
Would you like to bookmark or share a page and its specific part that you selected? You don't even need to modify the webpage.
What types of pages does it work with? See LinkToSelection.
Clone recursively:
git clone --recurse-submodules https://github.com/Focus4you/SelectionFirefox.git
or immediately after clone:
git submodule update --init --recursive.
That will leave submodule LinkToSelection in a 'detached HEAD.' You may want to switch it to master:
cd SelectionFirefox
cd LinkToSelection
git checkout master
For development of Firefox add-on, see Development Tools.