Netmarketshare's browser market share has just been updated to include May 2018 share information.
The company recorded a drop below the 10% mark in the desktop and laptop devices market for the Mozilla Firefox browser.

Firefox had a market share of 12.63% in June 2017 according to Netmarketshare
and even managed to rise above the 13% mark in 2017 before its share fell to 9.92% in May 2018.

以下ソース

Firefox dropped below the 10% share value on Netmarketshare
https://www.ghacks.net/2018/06/04/firefox-dropped-below-the-10-share-value-on-netmarketshare/