It has long been the case that nations blame their neighbours - especially those very close and against whom wars have been fought - for all sorts of failings. Thus, we make fun of �Dutch courage', which appears only if the Dutchman is drunk. Similarly, our slang for a condom includes the word �French' and theirs includes �English'. (We have 'letter' and they have 'overcoat'; the latter seems to make rather more sense, I have to say!) When we skive off, we take �French leave' and when they do, they take �English leave'.
'French' has also been used as an adjective in English to suggest 'spicy/sexy/naughty' since the early 18th century, in the belief that French people were somehow much more racy in such matters than the less outgoing British.
The actual 'FL' phrase is first recorded in English in the 1850s. It certainly does not offend me, but then I'm not the AB Editor and it may be that younger site-users are being 'protected'.