Using it with more than 10 tabs open can be painful. (It freezes redrawing whole firefox, unless you start moving your mouse over it, drop down menus sometimes completly stop appearing (only the shadow is being drown for example) and many more issues). Its a CPU Hog. Without i can have like 200 tabs opened and 30 clips playing on youtube at the same time and with it its hard to brows internet at all not to mention watching any videos. Also- sorry for my bad english.
I also like this plug-in as a self-teaching Japanese student but like ashemedai and 001Asoer I have a huge CPU being used. I already had this problem once but didn't really understood which plugins did it so I decided to desactivate some of them including XHTML Ruby Support and hurray ! It was fine. Recently, I decided I wish to read texts with furigana to help otherwise I just hardly feel like having the will to read japanese as i have a quite poor level and so I reactivated the plugin. There are sites where the PC becomes too slow, 100 % CPU or about. I noticed that on the site it begans using CPU there are many ruby data but for me it doesn't explain the behaviour because a text in japanese may have much more ruby that the site I was talking about. I wished to talk about the problem on that page but I see I'm not the only one and while I was searching I found an alternative to test.
In general I love this addon, but totday I had to turn it off because I managed to trace my Firefox stalls and 100% CPU core pegs to this addon.
I have no idea what exactly is going on, but the addon will cause a CPU core to continuously use 100% resources. Closing the tab will not solve anything since it seems the thread does not get ended. You have to restart Firefox completely.
This doesn't work for my version of Firefox 3, but I can tell you that it is an absolutely vital extension without which Firefox makes an embarrassingly terrible job of dealing with a key part of the XHTML spec.
Just installed it to read some texts of http://www.aozora.gr.jp. It looks great, even the line-height remains balanced in the pages I looked at so far. It must have been rather difficult to get everything right. However, I hope that in the end ruby support will give more options to the user. For example the option to toggle between different kinds of display. Like furigana versus popup text - or at least the option to disable the function with one click, since it may not always be compatible with certain website layouts. And it is not compatible with the fixed size bitmap font I normally use to read Japanese. But with a TTF it looks, like I said, great. Thanks!
I'm surprised this hasn't been rated. This is really wonderful. I hope it makes it into the Firefox trunk as Ruby is part of XHTML!
One thing that kept me away from ruby before was thinking that it was only for east Asian languages. But as the official W3C specs indicate, it can be used for annotating any foreign language script, or actually for annotating any text--like a multi-track but for text! (and it is not only more semantic than using a plain "table" element but unlike a table element, ruby text can wrap around--e.g., when the window is resized).
Now East Asian language fans will just need to wait for CSS3 with vertical text support (via stylesheets) to really round out the options.
Tip: check out http://www.w3.org/2002/12/09-rdf-docs/xhtml-math-svg-rdf-CC-flat.xhtml test out the extension (though this sample doesn't wrap the text).