STEPS TO REPRODUCE
(using a fresh profile)
1. load https://bugzilla.mozilla.org/
2. click Search
3. click Advanced Search
4. click Detailed Bug Information
5. click the Comment combobox
"contains all of the strings" is the only item in the menu.
Reloading the page fixes it.
PLATFORMS AND BUILDS TESTED
Firefox nightly on OSX
I suspect that the bug only occurs when the <select> is initially "display:none"
and then later (step 4) is made visible.
Reproduced with GTK.
It seems that toggling display style value isn't enough to reproduce this bug.
I've seen this a few times when going to plus a r? patch. I think it has been when using the spliter review tool in bugzilla. However it doesn't happen consistently enough that I think it's purely a function of setting CSS properties.
Bug 780661 will fix this hopefully.
Fixed by bug 780661.