I recently experienced an issue where Firefox was automatically trying to force an update of Flash even though I had automatic update turned off. As a result, my selenium scripts would fail because the browser would prompt for confirmation for updating flash and there was no one on the other side answering the prompt. To handle addon updates failing, Mozilla introduced a hang-ui.exe feature desing ed to kill hanging updates. Problem was, the update would hang until a timeout was reached, then the hang-ui.exe wouldlaunch and wait 45-60 more seconds with another prompt that would allow an attended user to kill the update. Still, no one was on the other side to answer the prompt. So Mozilla built hang-ui.exe to try for 45-60 seconds ... then afterwards, try killing the update again. It works ... but the problem is, my scripts navigate to many pages, and after 3-4 more page navigations, the update confirmation would come back. Ultimately, my scriptws would fail and show very high transaction times.
The solution for me was to enter about:config for the profile I am using and turn off the plugin check. Find the entry plugin.scan.plid.all and double-click on it to set it to false.
I verified that this worked for at least two tests ... the update.exe did not appear any longer.
Update: Also remember to deselect the "Update Addon's Automatically" setting under the configuration icon in the Add-ons Manager. Looks like this:
I have also installed the addon checkCompatibility version 1.3, which "Reinstates the extensions.checkCompatibility preference".