I've prepared a small sample app (attached below), which can reproduce the problem. At least I was able to reproduce it on two machines (physical and VM). The problem is, that it reproduces mainly the first error (published below) and only rarely second error. However, in my production tests, I see mainly the second issue

Most of the time I'm getting this error:
But from time to time, I'm getting also this error:LineageGlueRule 'firefox_web_child_elements' caused RanorexException on Execute. Error in MsgHostDom call: Tab id does not exist
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Ranorex.RanorexException: Error in MsgHostDom call: Tab id does not exist System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg,IMessage retMsg) +0x27 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData,Int32 type) +0x1b3 Ranorex.Plugin.IDom.GetDocumentChildren(Int32 wndId,Int32 tabId,Int64 frameId) +0xffffffff Ranorex.Plugin.FirefoxIpc.FirefoxDom.GetDocumentChildren(Int32 wndId,Int32 tabId,Int64 frameId) +0x0 Ranorex.Plugin.FirefoxWebChildrenRule.Execute(GlueRuleExecutionState state) +0xf Ranorex.Core.ElementEngine.ApplyGlueRules(Element element,GlueRuleExecutionStateImpl state,Boolean includeRemotes) +0x6a
LineageGlueRule 'firefox_web_child_elements' caused RanorexException on Execute. Message timeout reached.
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Ranorex.RanorexException: Message timeout reached. System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg,IMessage retMsg) +0x27 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData,Int32 type) +0x1b3 Ranorex.Plugin.IDom.GetFrameElementFrameId(NpPtr elemId) +0xffffffff Ranorex.Plugin.FirefoxIpc.FirefoxDom.GetFrameElementFrameId(NpPtr elemId) +0x0 Ranorex.Plugin.FirefoxWebFlavorElement.get_FrameElementFrameId() +0x8 Ranorex.Plugin.FirefoxWebChildrenRule.Execute(GlueRuleExecutionState state) +0x10e Ranorex.Core.ElementEngine.ApplyGlueRules(Element element,GlueRuleExecutionStateImpl state,Boolean includeRemotes) +0x6a