Keep getting the following message when switching from one tab to another in a proprietary application:
XXX 400 Bad Request (where XXX represents application)
Your browser sent a request that this server could not understand
Size of a request header field exceeds server limit.
Cleared caches and cookies but error returns.
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If clearing cookies doesn't work then it is possible that the cookies.sqlite file that stores the cookies is corrupted.
Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookie files like cookies.sqlite-journal in the Firefox profile folder in case the file cookies.sqlite got corrupted.