I will be off topic as what I am going to suggest is not open source… But I myself looked for a long time what was the best free windows file manager and I settled up on FreeCommander.
By default UI is not nice but it’s possible to make it nice enough.

I use this one mainly because : you can use it for free, dual pan, it remembers tab history between sessions, tabs can be renamed and colored. Hope someone will suggest a good open source one but I don’t think there is any :-/

I don’t understand the down votes
=> I always read up and down votes as a tool to flag valuable posts. It feels like down vote on this one is about agreement with the news?

On my work computer I don’t have admin rights but still I could install Firefox with no problems. It installed itself for local user only.

About that you can check this new extension : https://addons.mozilla.org/en-US/firefox/addon/chrome-mask/

Yet I feel it’s better to avoid using it and report web compatibility problems. Always masking user agent could led to believe only supporting chrome is sufficient.