Sure!
For Firefox:
For Chrome:
Another plugin which does the same thing and is easier to use (and seems to be more popular) is “Substital”. I don’t particularly like the font Sustital uses for Japanese or the positioning of the subtitles on the screen (the add-on lets you change font size, color, and background color, but not font face or position), so I use +Sub instead most of the time since its defaults work for me.
Both plugins require subtitle files to be in SRT format, but there are a number of programs out there that can convert other types of subtitle files to SRT.