For those of you who have been happily running Mark My Links and noticed that its configuration page stopped working on upgrading from Firefox 18.104.22.168 to 22.214.171.124 recently, I tracked down the regression today and found a work-around. The script has been updated now.
It boils down to the slight E4X shortcoming of not really supporting (I believe -- corrections warmly welcome) a way of writing a tag literal with a dynamically decided presence of some attribute -- as you want to do when generating a checkbox tag that either is checked or not (<input type="checkbox" checked="yes"/> vs <input type="checkbox"/>).
To do this, I kludged a solution that adds a harmless unchecked="yes" attribute when not checked, and this broke in 126.96.36.199 under particular conditions. Reordering the attributes to feature the dynamically named attribute last kludged the kludge to work again.
More exact technicalities in the bugzilla ticket.