If anyone’s wondering why, it’s called ateji: writing foreign loanwords with kanji that have similar sounds but not necessarily much correspondence in meaning. Nowadays people just write things using katakana (a phonetic script where each character represents a single syllable), but ateji used to be the standard. That said, it’s still very common to see single-character abbreviations for countries which use the first character of their ateji names (e.g. 独 for Germany, 豪 for Australia, and the aforementioned 仏 for France) in headlines as well as compounds like 日豪にちごう関係かんけい (Japan-Australian relations) or, apparently, 仏式ふつしきバルブ.