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Summary
The article describes UFT add-in for browser Mozilla Firefox and which object model they used.
Question
UFT (Unified Functional Testing) supports two Add-ins for Mozilla Firefox. The first one is HPE functional testing Legacy Agent and the second one is the UFT Agent that is installed by default with the UFT installation.
HPE functional testing Legacy Agent should be used when working with Mozilla Firefox 39 or its earlier versions. This Agent uses XPCOM that is a cross platform component object model, which works mainly with COM and can be used for running test on Java Applets too.
For more details regarding the XPCOM platform component object model please see the following article:
UFT Agent Add-in supports Firefox version 33 and higher. It mainly uses JavaScript and if there are any JavaScript errors within the source of the application that has been tested, that will break the communication bridge between UFT and UFT Agent Add-in in Firefox. What you may expect in such situation is to see UFT not responding for a while (it can be referred as freeze or hang of UFT). In case your UFT is not responding (freezing, hanging) and you do test against an application in Firefox then please check the Firefox Console log for any errors or warnings made by the application under tests and address them. If they are not addressed then it may be expected to experience freeze/hang of UFT.
For more information regarding Mozilla Browser Console, please see the article: