Both firefox 54 and 55 are, on USB stick, fast in anonymous navigation but slow in not anonymous navigation !! It's a disappointment .... Why ??
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Firefox 55 portable very slow
I blame Mozilla for the slowness, slowly migrating to QupZilla..now apparently called Falkon;
http://blog.qupzilla.com/2017/08/qupzilla-is-moving-under-kde-and.html#c...
and K-Meleon, as it too has its uses and seems faster than Firefox now.
Some times I blame the USB 2.0 connection and yearn for a true SCSI port.
At the end of this days session I'll do another Data only backup [and once every 2-3 days] and when I can get more removable media, re-install fresh copies of all my Portable Apps programs {clean,fresh profiles} then use the restore option to see if any of the old stuff became corrupt over the past four years.