Tor Browser / Firefox degrades into resourse hog
Bugzilla is full of similar bugs
CC(T+206349.0) max pause: 1891ms, total time: 2105ms, slices: 39, suspected: 457, visited: 32356 RCed and 273549 GCed, collected: 8121 RCed and 57395 GCed (57395|0|304 waiting for GC)
ForgetSkippable 19 times before CC, min: 0 ms, max: 47 ms, avg: 8 ms, total: 157 ms, max sync: 0 ms, removed: 6522
Some guys suspect NoScript, others - HTTPSE, but it's worth testing from the Tor Browser's side too. (It happens with an ordinary browsing of Trac and Bugzilla.)