Firefox constantly "freezes," not opening new tabs

Recently Firefox started "freezing" several times a day, refusing to open new tabs or refresh most old ones. When this happens I have to close Firefox, wait a minute (it won't re-open quickly), and re-open. I've tried steps 1-5 at https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems and nothing has worked. I've checked the Task Manager when this is happening and nothing seems to be slowing it down. I'm hesitant to get into #6. The same thing started happening maybe 6 months to a year ago. I got so frustrated I decided to abandon Firefox entirely and exported all my bookmarks to Chrome. Several months later I tested the waters again and it has been working fine, until now - same thing. Any ideas? I like keeping Chrome as my personal browser and Firefox for work.