Enter about:config into Firefox's address bar and press Enter.
Search for these files and change the value
content.max.tokenizing.time=2250000 (New integer value)
content.notify.interval=750000 (New integer value)
content.notify.ontimer=true (New boolean value)
content.notify.backoffcount=5 (New integer value)
content.switch.threshold=750000 (New integer value)
nglayout.initialpaint.delay=0 (New integer value)
content.interrupt.parsing=true (New boolean value)
browser.cache.memory.capacity=65536 (New integer value)
places.frecency.unvisitedBookmarkBonus=0
browser.urlbar.maxRichResults=-1
browser.urlbar.formatting.enabled=False
browser.urlbar.trimURLs=False
extensions.checkCompatibility=False (New boolean value)
layout.spellcheckDefault=2
browser.ctrlTab.previews=True
config.trim_on_minimize=True (New -> Boolean)
after this restart browser
