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If your firefox address bar is getting a bit slow and laggy as it tries to find suggestions, I found one single about:config tweak totally sorted it out for me.

browser.urlbar.search.timeout = 100

change to

browser.urlbar.search.timeout = 10

To do this, open a new tab and type about:config

Then agree to the thing that says you know what you are doing and in the filter bar at the top type:

urlbar.search.timeout

you can then double click on the value (set to 100 by default) and change it to whatever you want. I tried 10 and that seems to work great for me, but you might want to experiment.