I updated to Firefox 28 and all my add-ons were retained. Admittedly I only have a few and firefox automatically checked them to see if they were compatible with the updated version of the Browser.
Come the end of this month and Firefox 29 is being released and it is already being advertised as something which is going to be special.
sunny-dave - did you try Classic Theme Restorer https://addons.mozilla.org/en-US/firefox/addon/ClassicThemeRestorer/ ? I'm interested to know if it makes a significant difference. And, by the bye, if you have a 64bit machine then Palemoon (my current default browser) is apparently not going to be updated to use the new interface but can't confirm this.
I was so horrified by the all the changes that I just made my excuses and left, Bibble - it just used up so much of the precious real estate at the top of my netbook screen that it was like working in a letterbox.
I use various add-ons to make the display how I want it and I suspect that they are all going to be invalidated by the upcoming release, which is why I have switched to Palemoon for now.
p.s. to make sure that Add-ons do not disappear with a new update https://addons.mozilla.org/en-US/firefox/addon/checkcompatibility/ will ensure that they all carry on working - there is always a small chance that an affected add-on might misbehave after the update but I haven't once had that problem during the long time that I have been using that compatibility add-on.
@sunny-dave....Firefox 29 is Not being released until 29th April, consequently it is possible that your problems were, as mentioned above by Ratter15^^^ You were on the Beta Channel.
For info, whilst my Desktop is using Firefox 28, my laptop is on the Firefox 29 Beta and neither have presented me with real problems.( occasional freeze for a minute or so is about all)
Windows 7 or 8 - depends on machine - the issue isn't with the Op System.
I currently have FF28 customised so that it gives me the menus and bookmarks bar and search/address box all on a single line - with the tabs immediately below - thus wasting as little as possible of the vertical space on my screen.
I couldn't get this to work on FF29 - the best I could do was taking nearly twice the screen depth compared to FF28. This is a real handicap when using a 10.1" netbook where every cm of vertical screen space is useful for the actual web-page content.
@sunny-dave.....Yes I now see what you mean. Hopefully you have your Firefox Browser 'Options' set in the 'Advanced' section with enabled....'Check for up-dates but let me choose whether to install them'.