Follow-up from bug 1251809, In non-e10s, popup.xml will show the filenames of selected files in a tooltip. If there are more than 20 files selected, it will have "and X more files" appended to the end of the tooltip. In e10s, DefaultTooltipTextProvider::GetNodeText builds this list but can't add the "and X more files" because the string definitions for "and X more file;and X more files" are defined in PluralForm syntax which isn't supported from native code. The popup.xml code will only show the "and X more files" if there are 2 or more files over the limit, which means we could naively just use the "and X more files" string from C++. This may be naive (and I could be wrong), but it is my understanding that some languages have different plurality rules and would use different strings for 2 units, 3 units, etc., so having one string for all extra units would not suffice.