haha, all visible signs of the infection are now removed (including the accessing of the website when starting up firefox). Have you taken a look at the zip file and the malwarebytes website blocked.txt and the zip C.7z ?
look in your malwarebytes settings. If I recall correctly they actually act like the virus's they are supposed to stop and inject their own code into the running process. This also has a side effect of making the program unstable and prone to freezing and crashing. Undoubtedly it will be like all the times in the past and their addons is simply not compatible with Thunderbird 78 which drastically restricts addons access to the programs source to try and reduce the instability these type of things cause.
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