You won’t lose any of your bookmarks or browsing history, but some of your extensions and other add-ons might not work until updates for them are made available.
Losing extensions and/or add-ons would not be acceptable.
Why would you even do the update if you did not address extensions and add-ons?
Tutte le risposte (1)
There are thousands of extensions.
Put another way there are thousands of extensions that are useless to me. There are thousands of extensions that I don't use and have not seen.
Mozilla (if that is what you mean by you) can't hold up a release because extensions have not been updated. Extensions are the responsibility of their authors not of Mozilla.
If you mean why would a user do an update and lose extensions
- sometimes the update is forced on us
- sometimes the missing extensions are trivial or can be substituted.
I find your question a bit vague. I tried to answer two interpretations of it.
If you want to find out what is compatible for what you've got there is
Is It Compatible? :: Add-ons for Firefox