Dear Yutaka,
Well, I have now the Beta 4 version, so I’ll upgrade to Beta 6 and retest.
As for the button: it is there in Beta 4. In fact, it was the default. I didn’t customized it to be there. I did a window snapshot with it, but I don’t have a site to post it to and provide its URL. Is there a way to post it otherwise?
Regarding the Context Menu: you are right, FF does only features the “Add to Dictionary” and suggested replacements. But, as a user of MS Word where “Ignore all” is there, I can testify that this is very helpful. Sometimes you are dealing with an esoteric and temporary issue. If you don’t want to burden your dictionary with all these short-lived terms, “Ignore all” is very handy.
For your consideration,
Regards,
Meir