Jstools + Garland Theme + Firefox 2.0 Interference

I don't know if this bug has been reported or experienced before, but I just found out, that Jstools is triggering for the following problem:

I'm running Drupal 5.1 using the Garland theme. As soon as I activate the Jstools module (just 'Jstools core' module is sufficient) I have problems with collapsible fieldsets. If I expand fieldsets, which are collapsed by default, I can't click the buttons (Preview, Save, ...) at the bottom of a form anymore. If I move the cursor over the buttons it has the 'text input'-shape as if it was placed over a textfield/textarea. It seems like there's an invisible DIV or other element(s) covering the buttons, preventing them to receive mouse events. In order to be able to click the buttons at the bottom, I have to collapse the fieldsets I expanded, again.

Sometimes (can't remember where) I experienced the following oddities, too:
I clicked inside a textarea/textfield (a textarea/textfield which lives inside a fieldset I expanded) and started typing in text, but the text I typed was not drawn inside the textarea/textfield but some lines below (and outside) the textarea/textfield.

I did some testing and I only experience these problems using Firefox (2.0). I also tested with Konqueror and Internet Explorer, which don't produce these problems. I did not test all themes, but if I switch to another theme (e.g. bluemarine) expanded fieldsets don't cause trouble (using Firefox) anymore.

These are my observations, but I don't know if Jstools, Garland Theme, Firefox or the combination of those three is the reason for this strange behavior.