I stayed on FF 12.0 where all the most valuable addons still work. Some sites complained that I needed to upgrade the browser, so I changed the user agent string to:
Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:25.0) Gecko/20100101 Firefox/25.0
and told Firefox to stop updating. Here's how:
I run XP in virtual mode on VirtualBox in Ubuntu 10.04.4. A complete backup of the main XP vdi takes around 30 seconds, so I tend to do it often. If I do something stupid like install a bad program, or in the event that malware has downloaded itself, I simply save the current data files and overwrite the main vdi with the backup file. This takes only seconds. But I have had zero problems with malware.
I can send the vdi files to backup computers and have byte-identical copies running even though the motherboards, monitors, disk drives and everything else are completely different. You cannot do these things with an ordinary Windows installation.
I stay on XP due to compatibility problems with Win7. I don't waste time on antivirus programs that have low probabilility of detection and simply eat up cpu cycles and disk space.
I use Proxomitron to prevent malware from downloading, and System File Checker from Win98 to verify that none of the system files have been altered and there are no new files in any of the critical directories. I can also run Sysutils RootkitRevealer and similar programs to verify there are no rootkits installed. If malware tried to install in the boot sector, it would overwrite the Linux bootloader and I would have to reinstall Ubuntu.
I split Ubuntu into system files and a Home directory. Whenever I really screw up and have to reinstall Ubuntu, it only affects the root files. None of my setup and config files are harmed, and everything returns exactly the way I left it.
I can also copy all the Ubuntu configuration and setup to the backup computers so they are identical to my main computer. I never have to waste time fiddling with fonts, colors, system settings, or anything else to do with setting up the computers.
This is the way computing should be. No time wasted on silly configuration setups, hopelessly checking for malware, and no reinstallation of Windows that overwrites your data and program files.