Firefox 53 and Alert recognition (including WaitAlert) - default multi-process mode issue

Hello,

I've just (accidentally) upgraded my Firefox from version 47 or 48 or so to 53. I have the latest patch for TestComplete 12.30 to work with this version of Firefox. But I am now having problems with alert elements (in JScript) that I wasn't having before - I can't seem to use them at all. I'm trying .Alert and WaitAlert where they worked before and not having any luck with object recognition.

Is this a recognized issue with recent versions of Firefox? Have things changed?

Thanks for any help.

Alex