I've found a regression report on twitter, but I forgot to report it to bugzilla, sorry. https://twitter.com/Nymphium/status/509603095857201152 This is a regression of bug 479942. In bug 479942, we always set ' ' (U+20) to shortcut key candidate if the key event is caused by space bar. However, some users may assign other function key to space bar. In such case, we shouldn't scroll up/down the page. We should check WidgetKeyboardEvent::mKayNameIndex if it's value is KEY_NAME_INDEX_USE_STRING. If it's not so, that means the space bar is assigned to a function key.

Even if space key is pressed but it's assigned to a non-printable key, it shouldn't work as a space key because some users may assign Enter key or something to the space key. Review commit: https://reviewboard.mozilla.org/r/42563/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/42563/

Comment on attachment 8735066 [details] MozReview Request: Bug 1259679 - Space key shouldn't work as a space key if it's assigned to a function key. r?masayuki https://reviewboard.mozilla.org/r/42563/#review39073 r+ if tryserve detects no error. Thank you for your work!