How can I make Firefox stop forcing me to restart my browser?

Solution 1:

Go to 'about:config' and type in 'app.update' and you'll see a long list of configurable values. One of these is 'app.update.auto', which you can set to be FALSE, which should disable auto-updating alltogether.

Or perhaps you could alter the 'app.update.interval' value, which for me defaults to 43200 seconds, or 12 hours, and set this to a much higher value if you only want the auto update checked every month or even every year (31536000 seconds) as the OP requested.

Edit: It would be nice though if there was a configuration that checked and updated regularly but just stopped the forced restart.

Solution 2:

You can tell Firefox that you want it to stop automatically installing updates.

Use the "hamburger" menu (the three horizontal lines) in the upper right, then choose Options.

Then, in the General section, scroll down to the Firefox Updates section. Change to the Check for updates but let you choose to install them option:

While some have reported that this option has been removed, it still shows up in Firefox 81.0 (64-bit, Windows).

Other systems, perhaps where the system's own package manager is responsible for keeping Firefox up-to-date, do not show the option (screenshot is from a 64-bit Linux system):

Disclaimer

Preventing software from being kept up-to-date is not a good security practice. It is strongly recommended that you let the updating mechanism do its thing. If you only update once a year, it is likely that more than just "your flow" will get broken.