John is right. Here's the explanation from the forum software developers:
"When you upgrade to Firefox 2, you may notice that ALT+S suddenly opens the history menu and that ALT+P no longer triggers the preview button.
This is due to a new change in how Firefox handles accesskeys. Since both browsers and websites may want to use the same accesskeys, the developers decided to split the configuration option that specified what key to use for accesskeys into two different ones:
ui.key.chromeAccess - specifies which key (or combination of keys) triggers browser accesskeys
ui.key.contentAccess - specifies which key (or combination of keys) triggers website accesskeys
For whatever reason though, they felt that it was more important to make browser accesskeys override website accesskeys. Therefore, the default functionality in Firefox 2 has website accesskeys assigned to alt+shift. What's even more surprising is that the folks in charge didn't feel that it was important enough to mention in the release notes or the known issues.
Anyway, to fix this, open up a new tab, type about:config in the address bar and hit enter.
Welcome to the advanced Firefox settings area! Lots of nifty stuff here.
Type access into the filter bar
Double-click on ui.key.contentAccess and set its value to 4.
This will make browser and content accesskeys have the same alt+key combination, but will make the content accesskeys have more precedence than the others.
For more information on possible values for this setting, see
this."