Squashed 'lib/' changes from f8063fe..899d396

899d396 Make Curl dependency optional
ced8c1f Rename LIB_DIR constant in FF_LIB_DIR

git-subtree-dir: lib
git-subtree-split: 899d39673058b7f06f221f14504d7398f3611e9b
Merge commit '2592c8d83ce0f8b95a621761ad3bc704b278facf'
Adapted changes in library